/* DesignOS — "Aurora Glass" stylesheet. Premium, Apple-like, glassmorphic. Dark-first with a
   polished light option. Muted cool palette (no neon), frosted surfaces, restrained type. */

* { box-sizing: border-box; margin: 0; padding: 0; }
html, body { background: #0B0D11; }

:root {
  /* Light — polished, muted, glassy */
  --bg: #F4F6F9; --surface: #FFFFFF;
  --surface-alt: #EDEFF3;
  --card-bg: #FFFFFF; --card-brd: #E4E8EF;
  --mint: #EAF1EC; --lav: #ECEEF6; --peach: #F6F0E9; --sky: #EAF0F7;
  --ink: #14161B; --ink2: #5B6270; --border: #E4E8EF;
  --accent: #445E86;
  --accent-2: #54648C;
  --on-accent: #FFFFFF;
  --accent-soft: rgba(68,94,134,.10);
  --accent-line: rgba(68,94,134,.24);
  --prog-grad: linear-gradient(90deg, #6E86B4, #445E86);
  --btn-bg: #14161B; --btn-ink: #FFFFFF;
  --gold: #9A7B33;
  --success: #3F7D5E; --warn: #7A5F27; --warn-soft: rgba(154,123,51,.12); --error: #B5453B;
  --serif: 'Inter', system-ui, sans-serif;
  --display: 'Inter', system-ui, sans-serif;
  --prose-font: 'Inter', system-ui, sans-serif;
  --shadow1: 0 1px 2px rgba(16,18,24,.04), 0 16px 38px -16px rgba(16,18,24,.14);
  --shadow-lift: 0 2px 8px rgba(16,18,24,.06), 0 30px 60px -24px rgba(16,18,24,.22);
  --glow: 0 14px 40px -16px rgba(68,94,134,.28);
  --glass: rgba(255,255,255,.70); --glass-brd: rgba(255,255,255,.6); --blur: blur(22px) saturate(1.4);
  --edge: inset 0 1px 0 rgba(255,255,255,0);
  /* warm hover tint — a mild orange glow on interactive hover, distinct from the
     cool periwinkle used for active/selected states */
  --hover-glow: rgba(240,150,70,.15); --hover-line: rgba(240,150,70,.46); --hover-ink: #9C5410; --hover-soft: rgba(240,150,70,.10);
  --pad-card: 22px; --row-h: 52px;
  /* Corner radius: three tokens, everywhere — 4 (controls/checkboxes), 8 (buttons/
     inputs/chips), 16 (cards/panels). Circular controls use 50% instead, a separate
     shape decision, not a fourth radius. */
  --r-sm: 4px; --r-md: 8px; --r-lg: 16px;
  --r-card: var(--r-lg); --r-btn: var(--r-md);
  --r-font: 1; --r-lh: 1; --r-measure: 720px;
  --sidebar: #14151A; --sidebar-ink: #9A9CA6; --sidebar-active-bg: rgba(255,255,255,.10); --sidebar-active-ink: #FFFFFF;
  --nav-bg: #FFFFFF; --nav-ink: #5B6270; --nav-active: var(--accent-soft);
  --aurora:
    radial-gradient(1100px 620px at 8% -10%, rgba(88,110,150,.09), transparent 60%),
    radial-gradient(980px 540px at 102% -4%, rgba(110,120,160,.07), transparent 56%),
    radial-gradient(880px 700px at 96% 104%, rgba(120,130,170,.06), transparent 60%);
}

/* Dark — the default premium look (matches the glass inspiration) */
.dark {
  --bg: #0B0D11; --surface: #14171D; --surface-alt: #1A1E25;
  --card-bg: rgba(255,255,255,.045); --card-brd: rgba(255,255,255,.09);
  --mint: #16211C; --lav: #171A22; --peach: #221D17; --sky: #141A22;
  --ink: #EEF0F4; --ink2: #9CA3B0; --border: rgba(255,255,255,.09);
  --accent: #9DB0D6;
  --accent-2: #8494BE;
  --on-accent: #0B0D11;
  --accent-soft: rgba(157,176,214,.12);
  --accent-line: rgba(157,176,214,.26);
  --prog-grad: linear-gradient(90deg, #C6D2E8, #9DB0D6);
  --btn-bg: #ECEEF3; --btn-ink: #14161B;
  --gold: #D8B872;
  --success: #6FC79B; --warn: #D8B872; --warn-soft: rgba(216,184,114,.14); --error: #E88A82;
  --shadow1: 0 1px 2px rgba(0,0,0,.5), 0 20px 44px -18px rgba(0,0,0,.66);
  --shadow-lift: 0 2px 10px rgba(0,0,0,.55), 0 40px 80px -30px rgba(0,0,0,.75);
  --glow: 0 20px 60px -24px rgba(0,0,0,.6);
  --glass: rgba(20,23,29,.58); --glass-brd: rgba(255,255,255,.08); --blur: blur(26px) saturate(1.3);
  --edge: inset 0 1px 0 rgba(255,255,255,.06);
  --hover-glow: rgba(245,165,85,.18); --hover-line: rgba(245,165,85,.5); --hover-ink: #F2A661; --hover-soft: rgba(245,165,85,.12);
  --sidebar: #101318; --sidebar-ink: #9295A2; --sidebar-active-bg: rgba(255,255,255,.11); --sidebar-active-ink: #FFFFFF;
  --nav-bg: #101318; --nav-ink: #9CA3B0; --nav-active: var(--accent-soft);
  --aurora:
    radial-gradient(1200px 720px at 10% -12%, rgba(96,116,160,.16), transparent 58%),
    radial-gradient(1000px 560px at 104% -6%, rgba(78,96,140,.13), transparent 56%),
    radial-gradient(900px 760px at 98% 106%, rgba(120,110,160,.10), transparent 60%);
  color-scheme: dark;
}

.sepia {
  --bg: #F3ECDF; --surface: #FFFDF9; --surface-alt: #F3ECDF; --card-bg: #FFFDF9; --card-brd: #EAE0CF;
  --ink: #2A2116; --ink2: #6E6252; --border: #EAE0CF;
  --accent: #8A6A3A; --accent-2: #7A8560; --nav-bg: #FFFDF9;
  --prog-grad: linear-gradient(90deg, #A9884E, #8A6A3A);
  --btn-bg: #2A2116; --btn-ink: #FFFDF9;
  --sidebar: #221B10; --sidebar-ink: #A99878; --sidebar-active-bg: rgba(255,255,255,.12); --sidebar-active-ink: #FFF;
  --accent-soft: rgba(138,106,58,.12); --accent-line: rgba(138,106,58,.28);
  --glass: rgba(255,253,249,.72); --glass-brd: rgba(255,255,255,.5);
  --aurora: radial-gradient(1000px 560px at 6% -8%, rgba(138,106,58,.10), transparent 58%), radial-gradient(900px 520px at 100% 0%, rgba(122,133,96,.07), transparent 56%);
}
.amoled { --bg:#000000; --surface:#0a0a0a; --surface-alt:#131313; --card-bg:rgba(255,255,255,.04); --card-brd:rgba(255,255,255,.08); --ink:rgba(255,255,255,.92); --ink2:rgba(210,210,210,.6); --border:rgba(255,255,255,.08); --nav-bg:#000000; --glass:rgba(0,0,0,.6); --glass-brd:rgba(255,255,255,.06); --aurora:none; color-scheme:dark; }
.hc { --bg:#ffffff; --surface:#ffffff; --surface-alt:#f0f0f0; --card-bg:#fff; --card-brd:#000; --ink:#000000; --ink2:#1a1a1a; --border:#000000; --accent:#1c3d6e; --on-accent:#ffffff; --btn-bg:#000; --btn-ink:#fff; --prog-grad:#1c3d6e; --glass:#ffffff; --glass-brd:#000000; --aurora:none; }
.hc.dark { --bg:#000000; --surface:#0a0a0a; --surface-alt:#151515; --card-bg:#0a0a0a; --card-brd:#fff; --ink:#ffffff; --ink2:#e8e8e8; --border:#ffffff; --accent:#a9c2ee; --on-accent:#000000; --btn-bg:#fff; --btn-ink:#000; --prog-grad:#a9c2ee; --glass:#000000; --aurora:none; }

.sansprose { --prose-font: 'Inter', system-ui, sans-serif; --serif: 'Inter', system-ui, sans-serif; --display: 'Inter', system-ui, sans-serif; }
.serifprose { --prose-font: 'Source Serif 4', Georgia, serif; --serif: 'Source Serif 4', Georgia, serif; --display: 'Inter', system-ui, sans-serif; }

html { background-image: none; background-attachment: fixed; }
body { font-family: var(--prose-font); }
button, input, textarea, select { font-family: inherit; color: inherit; }
a { color: inherit; }
::selection { background: rgba(157,176,214,.24); color: inherit; }

/* Premium scrollbars */
* { scrollbar-width: thin; scrollbar-color: rgba(140,146,160,.4) transparent; }
*::-webkit-scrollbar { width: 10px; height: 10px; }
*::-webkit-scrollbar-thumb { background: rgba(140,146,160,.34); border-radius: 16px; border: 2px solid transparent; background-clip: padding-box; }
*::-webkit-scrollbar-thumb:hover { background: rgba(140,146,160,.56); background-clip: padding-box; }

.dos :focus-visible, .dos button:focus-visible, .dos a:focus-visible, .dos input:focus-visible, .dos textarea:focus-visible, .dos select:focus-visible {
  outline: 2px solid var(--accent); outline-offset: 2px;
}
.reading-mode .dos-sidebar, .reading-mode .dos-header { display: none !important; }
.reading-mode main.dos-main { padding-top: 32px; }
.warmth-overlay { position: fixed; inset: 0; pointer-events: none; z-index: 5; mix-blend-mode: multiply; }

/* ---------- shell + aurora ground ---------- */
#dos-root { position: relative; min-height: 100vh; background: var(--bg); color: var(--ink); font-family: var(--prose-font); font-size: 16px; line-height: 1.5; display: flex; align-items: stretch; }
/* living aurora — parallaxes with the mouse + scroll (driven by fx.js) */
#dos-root::before { content: ''; position: fixed; inset: -10%; z-index: 0; pointer-events: none; background: var(--aurora); transform: translate3d(var(--aurx,0px), var(--aury,0px), 0) scale(1.08); }
/* film grain overlay */
#dos-root::after { content: ''; position: fixed; inset: 0; z-index: 0; pointer-events: none; opacity: .03; mix-blend-mode: soft-light;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='140' height='140'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E"); }
.amoled #dos-root::after, .hc #dos-root::after { display: none; }
@keyframes dosAuroraDrift { 0% { transform: translate3d(0,0,0) scale(1); } 100% { transform: translate3d(-3%, 2%, 0) scale(1.08); } }
.reduce-motion::before { animation: none !important; }
@media (prefers-reduced-motion: reduce) { #dos-root::before { animation: none !important; } }

.dos-sidebar { position: sticky; z-index: 3; width: 224px; flex: none; top: 0; height: 100vh; display: flex; flex-direction: column; padding: 24px 16px 16px; margin: 16px 0 16px 16px; border-radius: 16px; background-image: linear-gradient(180deg, rgba(255,255,255,.05) 0%, rgba(255,255,255,0) 40%); background-color: var(--sidebar); border: 1px solid rgba(255,255,255,.07); box-shadow: 0 30px 70px -30px rgba(0,0,0,.7), inset 0 1px 0 rgba(255,255,255,.07); }

/* Logo */
.dos-sidebar-logo { padding: 4px 8px 32px; }
.dos-logo { display: flex; align-items: center; gap: 16px; width: 100%; margin: 4px 4px 32px; padding: 0; background: none; border: none; cursor: pointer; transition: transform .3s cubic-bezier(.2,.9,.3,1), opacity .2s; }
.dos-logo:hover { transform: translateY(-1px); }
.dos-logo:active { transform: scale(.98); }
.dos-logo-mark { width: 34px; height: 34px; flex: none; border-radius: 8px; display: grid; place-items: center; color: #fff; background-image: linear-gradient(150deg, rgba(255,255,255,.20), rgba(255,255,255,.03)); border: 1px solid rgba(255,255,255,.16); box-shadow: inset 0 1px 0 rgba(255,255,255,.22), 0 6px 16px -8px rgba(0,0,0,.6); transition: transform .4s cubic-bezier(.2,.9,.3,1), box-shadow .3s; }
.dos-logo:hover .dos-logo-mark { transform: scale(1.07); box-shadow: inset 0 1px 0 rgba(255,255,255,.28), 0 10px 24px -8px rgba(0,0,0,.7), 0 0 0 4px rgba(255,255,255,.05); }
.dos-logo-orbit { transform-box: view-box; transform-origin: 12px 12px; }
.dos-logo:hover .dos-logo-orbit { animation: dosOrbit 2.2s linear infinite; }
@keyframes dosOrbit { to { transform: rotate(360deg); } }
.dos-logo-word { font-family: var(--display); font-weight: 600; font-size: 18px; letter-spacing: -.01em; color: #fff; }
.dos-logo-word b, .dos-logo-word .hl { font-weight: 700; }

.dos-sidebar nav { display: flex; flex-direction: column; gap: 4px; }

[data-dos-nav] { transition: background .25s cubic-bezier(.2,.9,.4,1), color .2s ease-out, transform .18s cubic-bezier(.2,.9,.3,1); color: var(--sidebar-ink); position: relative; display: flex; align-items: center; gap: 16px; width: 100%; padding: 0 16px; height: 44px; border-radius: 8px; font-size: 14px; font-weight: 500; background: transparent; border: 1px solid transparent; cursor: pointer; text-align: left; }
[data-dos-nav] svg { flex: none; transition: transform .28s cubic-bezier(.2,.9,.3,1); }
[data-dos-nav]:hover { background: rgba(255,255,255,.06); color: #fff; }
[data-dos-nav]:hover svg { transform: translateX(1px) scale(1.06); }
[data-dos-nav]:active { transform: scale(.985); }
[data-dos-nav][data-active="true"] { background: var(--sidebar-active-bg) !important; color: var(--sidebar-active-ink) !important; border-color: rgba(255,255,255,.14); box-shadow: inset 0 1px 0 rgba(255,255,255,.16), 0 8px 20px -10px rgba(0,0,0,.5); }
[data-dos-nav][data-active="true"] svg { color: #fff; }
[data-dos-nav]::after { content: ''; position: absolute; left: 6px; top: 50%; width: 3px; height: 0; border-radius: 16px; background: var(--accent); transform: translateY(-50%); transition: height .32s cubic-bezier(.2,.9,.3,1); }
[data-dos-nav][data-active="true"]::after { height: 17px; }

.dos-sidebar-foot { margin-top: auto; padding: 16px 8px 0; border-top: 1px solid rgba(255,255,255,.09); display: flex; align-items: center; gap: 16px; }
.dos-sidebar-credit { padding: 0 8px 16px; }
.dos-sidebar-credit a { font-size: 11.5px; color: var(--sidebar-ink); text-decoration: none; letter-spacing: .01em; transition: color .2s, opacity .2s; display: inline-flex; align-items: center; gap: 4px; }
.dos-sidebar-credit a::after { content: '↗'; font-size: 10px; opacity: .6; transition: transform .25s cubic-bezier(.2,.9,.3,1); }
.dos-sidebar-credit a:hover { color: #fff; }
.dos-sidebar-credit a:hover::after { transform: translate(2px,-2px); }

[data-tip] { position: relative; }
[data-tip]:hover::after { content: attr(data-tip); position: absolute; left: calc(100% + 12px); top: 50%; transform: translateY(-50%); background: var(--ink); color: var(--bg); font-size: 12px; font-weight: 600; padding: 8px 8px; border-radius: 4px; white-space: nowrap; pointer-events: none; z-index: 60; box-shadow: var(--shadow1); }

/* Rows set their resting background via --row-bg (a custom property), never the
   background shorthand directly — an inline `background:` declaration has higher
   specificity than any stylesheet rule and would permanently block :hover below. */
[data-dos-row] { transition: background .2s ease-out, color .2s; border-radius: 8px; background: var(--row-bg, transparent); }
[data-dos-row]:hover { background: var(--hover-soft); }
[data-dos-cardlink] { transition: border-color .22s cubic-bezier(.2,.9,.4,1), box-shadow .22s ease-out, transform .22s cubic-bezier(.2,.9,.3,1); }
[data-dos-cardlink]:hover { border-color: var(--accent-line); box-shadow: var(--shadow-lift); transform: translateY(-3px); }

.dos-eyebrow { font-family: var(--display); font-weight: 600; letter-spacing: .16em; text-transform: uppercase; color: var(--ink2); font-size: 11.5px; }
.dos-rule { border: none; border-top: 1px solid var(--border); }
.dos-prose { font-family: var(--prose-font); font-weight: var(--r-weight, 400); letter-spacing: calc(var(--r-ls, 0) * 1px); word-spacing: calc(var(--r-ws, 0) * 1px); text-align: var(--r-align, left); margin-bottom: calc(var(--r-ps, 0) * 1px); }

.reduce-motion * { animation: none !important; transition: none !important; }
.line-focus .dos-prose { opacity: .48; transition: opacity .15s ease-out; }
.line-focus .dos-prose:hover { opacity: 1; }

@keyframes dosPop { 0% { transform: scale(.97) translateY(6px); opacity: 0; } 100% { transform: scale(1) translateY(0); opacity: 1; } }
@keyframes dosBlink { 0%,100% { opacity: .3; } 50% { opacity: 1; } }
@keyframes dosSlideUp { 0% { transform: translateY(20px); opacity: 0; } 100% { transform: translateY(0); opacity: 1; } }
@keyframes dosFadeIn { 0% { opacity: 0; } 100% { opacity: 1; } }
@keyframes dosFloat { 0%, 100% { transform: translateY(0px); } 50% { transform: translateY(-8px); } }
@keyframes dosPulse { 0%, 100% { opacity: 1; } 50% { opacity: .5; } }
@keyframes dosShimmer { 0% { background-position: -1000px 0; } 100% { background-position: 1000px 0; } }
@keyframes dosSlideDown { 0% { transform: translateY(-18px); opacity: 0; } 100% { transform: translateY(0); opacity: 1; } }
@keyframes dosProgShimmer { 0% { transform: translateX(-100%); } 100% { transform: translateX(320%); } }

.dos-typing span { display:inline-block; width:6px; height:6px; border-radius:50%; background:var(--ink2); margin:0 4px; animation: dosBlink 1.2s infinite; }
.dos-typing span:nth-child(2){ animation-delay:.2s; } .dos-typing span:nth-child(3){ animation-delay:.4s; }

/* Cinematic section transition — plays only when the section/topic changes (fx.js) */
@keyframes dosSecEnter { 0% { opacity: 0; transform: translateY(12px) scale(.995); filter: blur(3px); } 100% { opacity: 1; transform: none; filter: blur(0); } }
main.dos-main.dos-sec-enter > * { animation: dosSecEnter .42s cubic-bezier(.16,.9,.3,1); }

/* Apple-style shared-element page transition (View Transitions API). The sidebar
   and header are named so they morph in place while the main content crossfades. */
@keyframes dosVtIn { from { opacity: 0; transform: translateY(14px) scale(.992); filter: blur(4px); } to { opacity: 1; transform: none; filter: blur(0); } }
@keyframes dosVtOut { from { opacity: 1; } to { opacity: 0; } }
::view-transition-old(root) { animation: dosVtOut .24s ease both; }
::view-transition-new(root) { animation: dosVtIn .46s cubic-bezier(.16,.9,.3,1) both; }
.dos-sidebar { view-transition-name: dos-sidebar; }
.dos-header { view-transition-name: dos-header; }
@media (prefers-reduced-motion: reduce) { ::view-transition-group(*), ::view-transition-old(*), ::view-transition-new(*) { animation: none !important; } }

/* Scroll reveal — armed on below-the-fold cards after each render (fx.js) */
.dos-reveal { opacity: 0; transform: translateY(32px); }
.dos-reveal.dos-in { opacity: 1; transform: none; transition: opacity .7s cubic-bezier(.16,.9,.3,1) var(--rvd,0s), transform .8s cubic-bezier(.16,.9,.3,1) var(--rvd,0s); }

.dos-scroll-fade { opacity: 0; transform: translateY(22px); transition: opacity .6s ease-out, transform .6s cubic-bezier(.16,.1,.3,1); }
.dos-scroll-fade.visible { opacity: 1; transform: translateY(0); }

button, [role="button"], [data-act] { position: relative; }
button:not(:disabled):active, [role="button"]:active, [data-act]:active { transform: scale(.98); }

/* .dos-card / .dos-card-16 are content containers, never the click target
   themselves — they carry no hover state at all. Only a genuinely clickable
   element (a button, [data-dos-cardlink], a lesson row…) gets hover feedback. */

.dos-loading { animation: dosShimmer 2s infinite; background: linear-gradient(90deg, var(--surface) 0%, rgba(255,255,255,.12) 50%, var(--surface) 100%); background-size: 1000px 100%; }
.dos-success { animation: dosPulse .6s ease-out; }
.dos-float { animation: dosFloat 3s ease-in-out infinite; }
.dos-h1, .dos-h1-lg { animation: dosSlideDown .6s cubic-bezier(.16,.1,.3,1); }

@media (prefers-reduced-motion: reduce) { .dos * { transition: none !important; animation: none !important; } }

/* ---------- header (glass) ---------- */
.dos-header { position: sticky; top: 0; z-index: 20; display: flex; align-items: center; gap: 16px; height: 66px; padding: 0 24px; border-bottom: 1px solid var(--border); background: var(--glass); -webkit-backdrop-filter: var(--blur); backdrop-filter: var(--blur); }
.dos-icon-btn { width: 44px; height: 44px; flex: none; display: flex; align-items: center; justify-content: center; background: var(--card-bg); border: 1px solid var(--border); border-radius: 8px; color: var(--ink); cursor: pointer; transition: transform .2s cubic-bezier(.2,.9,.3,1), border-color .2s, box-shadow .2s; }
.dos-icon-btn:hover { border-color: var(--accent-line); transform: translateY(-1px); box-shadow: var(--shadow1); }
.dos-search-btn { display: flex; align-items: center; gap: 8px; height: 44px; max-width: 360px; flex: 1; padding: 0 16px; background: var(--card-bg); border: 1px solid var(--border); border-radius: 16px; color: var(--ink2); font-size: 14px; cursor: pointer; text-align: left; transition: border-color .2s, box-shadow .25s, transform .2s; }
.dos-search-btn:hover { color: var(--hover-ink); border-color: var(--hover-line); box-shadow: 0 12px 34px -16px var(--hover-line); transform: translateY(-1px); }
.dos-search-btn span:first-of-type { flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.dos-kbd { flex: none; font-size: 11px; font-weight: 500; padding: 4px 8px; border: 1px solid var(--border); border-radius: 4px; color: var(--ink2); }
.dos-aa-btn { height: 44px; padding: 0 16px; flex: none; display: flex; align-items: center; gap: 8px; background: var(--card-bg); border: 1px solid var(--border); border-radius: 16px; color: var(--ink); cursor: pointer; font-family: var(--display); font-size: 15px; transition: transform .2s cubic-bezier(.2,.9,.3,1), border-color .2s, box-shadow .2s; }
.dos-aa-btn:hover { border-color: var(--accent-line); transform: translateY(-1px); box-shadow: var(--shadow1); }

/* ---------- generic card/row primitives ---------- */
.dos-card, .dos-card-16 { position: relative; background-color: var(--card-bg); background-image: linear-gradient(180deg, rgba(255,255,255,.035), rgba(255,255,255,0) 42%); border: 1px solid var(--card-brd); border-radius: var(--r-card); padding: var(--pad-card); box-shadow: var(--edge), var(--shadow1); }
/* cursor spotlight + 3D tilt (driven by fx.js via --mx/--my/--rx/--ry) — scoped to
   elements that are themselves a single click target, never a passive container. */
.dos-card, .dos-card-16, [data-dos-cardlink], .stat-tile.clickable, .dos-flip-card, .dos-lesson-row, .dos-continue { position: relative; }
[data-dos-cardlink]::after, .stat-tile.clickable::after, .dos-flip-card::after, .dos-lesson-row::after { content: ''; position: absolute; inset: 0; border-radius: inherit; pointer-events: none; opacity: 0; transition: opacity .35s ease; background: radial-gradient(420px circle at var(--mx,50%) var(--my,50%), var(--hover-glow), transparent 55%); }
/* actionable tiles: 3D tilt toward the cursor + warm hover edge */
.fx-tilt { transform: perspective(950px) rotateX(var(--rx,0deg)) rotateY(var(--ry,0deg)) translateY(-3px) !important; transition: transform .12s ease-out, box-shadow .3s, border-color .3s !important; box-shadow: var(--edge), var(--shadow-lift) !important; border-color: var(--hover-line) !important; }
.fx-tilt::after { opacity: 1; }
.dos-h1 { font-family: var(--display); font-size: 32px; font-weight: 600; letter-spacing: -0.022em; line-height: 1.12; }
.dos-h1-lg { font-family: var(--display); font-size: 46px; font-weight: 600; letter-spacing: -0.032em; line-height: 1.06; }
.dos-sub { color: var(--ink2); font-size: 15px; margin-top: 8px; }
.dos-btn-primary { position: relative; overflow: hidden; height: 44px; padding: 0 24px; border-radius: 16px; border: none; background: var(--btn-bg); color: var(--btn-ink); font-family: var(--display); font-size: 14px; font-weight: 600; cursor: pointer; box-shadow: var(--shadow1); transition: transform .2s cubic-bezier(.2,.9,.3,1), box-shadow .25s, opacity .2s; }
.dos-btn-primary::before { content: ''; position: absolute; top: 0; left: -80%; width: 55%; height: 100%; background: linear-gradient(100deg, transparent, rgba(255,255,255,.35), transparent); transform: skewX(-18deg); transition: left .6s cubic-bezier(.2,.7,.3,1); }
.dos-btn-primary:hover { transform: translateY(-2px); box-shadow: var(--shadow-lift); }
.dos-btn-primary:hover::before { left: 140%; }
.dos-btn-primary:disabled { opacity: .5; cursor: default; box-shadow: none; }
.dos-btn-soft { height: 40px; padding: 0 16px; border-radius: 16px; border: 1px solid var(--accent-line); background: var(--accent-soft); color: var(--accent); font-family: var(--display); font-size: 14px; font-weight: 600; cursor: pointer; transition: transform .2s cubic-bezier(.2,.9,.3,1), box-shadow .2s, background .2s; }
.dos-btn-soft:hover { transform: translateY(-1px); box-shadow: var(--glow); }
.dos-btn-outline { height: 44px; padding: 0 24px; border-radius: 16px; border: 1px solid var(--border); background: var(--card-bg); color: var(--ink); font-family: var(--display); font-size: 14px; font-weight: 500; cursor: pointer; transition: transform .2s cubic-bezier(.2,.9,.3,1), border-color .2s, box-shadow .2s; }
.dos-btn-outline:hover { border-color: var(--accent-line); transform: translateY(-1px); box-shadow: var(--shadow1); }
.dos-chip { height: 34px; padding: 0 16px; border-radius: 16px; border: 1px solid var(--border); background: var(--card-bg); color: var(--ink); font-size: 13px; font-weight: 500; cursor: pointer; transition: transform .18s cubic-bezier(.2,.9,.3,1), background .2s, border-color .2s, color .2s; }
.dos-chip:hover { background: var(--hover-soft); border-color: var(--hover-line); color: var(--hover-ink); transform: translateY(-1px); }
/* Resting look set via custom properties, not the background/border-color
   shorthands — an inline declaration of either would outrank :hover below. */
.dos-pill-btn { height: 36px; padding: 0 16px; border-radius: 16px; border: 1px solid var(--pill-brd, var(--border)); background: var(--pill-bg, var(--card-bg)); color: var(--accent); font-size: 13px; font-weight: 600; cursor: pointer; transition: transform .18s cubic-bezier(.2,.9,.3,1), background .2s, border-color .2s; }
.dos-pill-btn:hover { background: var(--hover-soft); border-color: var(--hover-line); color: var(--hover-ink); transform: translateY(-1px); }
.dos-progress { position: relative; height: 8px; border-radius: 16px; background: var(--surface-alt); overflow: hidden; }
.dos-progress > div { position: relative; height: 100%; border-radius: 16px; background: var(--prog-grad); transition: width .5s cubic-bezier(.2,.7,.3,1); overflow: hidden; }
.dos-progress > div::after { content: ''; position: absolute; inset: 0; width: 40%; background: linear-gradient(90deg, transparent, rgba(255,255,255,.4), transparent); animation: dosProgShimmer 2.6s ease-in-out infinite; }
.dos-breadcrumb { display: flex; align-items: center; gap: 8px; font-size: 13px; font-family: var(--prose-font); color: var(--ink2); flex-wrap: wrap; }
.dos-breadcrumb button { background: none; border: none; color: var(--accent); font-size: 13px; font-weight: 500; cursor: pointer; padding: 4px 0; transition: opacity .15s; }
.dos-breadcrumb button:hover { color: var(--hover-ink); }

main.dos-main { position: relative; z-index: 1; flex: 1; padding: 24px 24px 120px; }
.dos-page { max-width: 1040px; margin: 0 auto; display: flex; flex-direction: column; gap: 24px; }
.dos-page-narrow { max-width: 760px; margin: 0 auto; display: flex; flex-direction: column; gap: 24px; }
.dos-page-mid { max-width: 820px; margin: 0 auto; display: flex; flex-direction: column; gap: 24px; }
.dos-page-gym { max-width: 900px; margin: 0 auto; display: flex; flex-direction: column; gap: 24px; }

.dos-grid-stats { display: grid; grid-template-columns: repeat(auto-fit,minmax(190px,1fr)); gap: 16px; }
.dos-grid-2 { display: grid; grid-template-columns: 1.6fr 1fr; gap: 16px; align-items: stretch; }
.dos-grid-3-auto { display: grid; grid-template-columns: repeat(auto-fit,minmax(240px,1fr)); gap: 16px; }
.dos-grid-2-eq { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.dos-grid-cards { display: grid; grid-template-columns: repeat(auto-fill,minmax(300px,1fr)); gap: 16px; }
.dos-grid-cards-sm { display: grid; grid-template-columns: repeat(auto-fill,minmax(260px,1fr)); gap: 16px; }
.dos-grid-badges { display: grid; grid-template-columns: repeat(auto-fill,minmax(150px,1fr)); gap: 16px; }
@media (max-width: 760px) {
  .dos-grid-2, .dos-grid-2-eq { grid-template-columns: 1fr; }
}

.stat-tile { position: relative; background-color: var(--card-bg); background-image: linear-gradient(180deg, rgba(255,255,255,.035), rgba(255,255,255,0) 42%); border: 1px solid var(--card-brd); border-radius: var(--r-card); padding: 16px 16px; display: flex; align-items: center; gap: 16px; text-align: left; cursor: default; color: var(--ink); box-shadow: var(--edge), var(--shadow1); transition: transform .22s cubic-bezier(.2,.9,.3,1), box-shadow .22s, border-color .22s; }
[data-dos-cardlink] { position: relative; }
.stat-tile.clickable { cursor: pointer; }
.stat-tile.clickable:hover { transform: translateY(-3px); box-shadow: var(--shadow-lift); border-color: var(--accent-line); }
.stat-tile .ic { width: 40px; height: 40px; flex: none; border-radius: 8px; background: var(--accent-soft); color: var(--accent); display: flex; align-items: center; justify-content: center; transition: transform .28s cubic-bezier(.2,.9,.3,1); }
.stat-tile.clickable:hover .ic { transform: scale(1.1) rotate(-4deg); }
.stat-tile .num { font-family: var(--display); font-size: 24px; font-weight: 600; font-variant-numeric: tabular-nums; line-height: 1.1; letter-spacing: -.02em; }
.stat-tile .lbl { font-size: 12.5px; color: var(--ink2); margin-top: 4px; }

/* ---------- topic page ---------- */
.dos-topic-progress { height: 3px; border-radius: 16px; background: var(--surface-alt); overflow: hidden; }
.dos-topic-progress > div { height: 100%; background: var(--prog-grad); transition: width .1s linear; }
.dos-example-card { background: var(--accent-soft); border: 1px solid var(--accent-line); border-radius: var(--r-card); padding: 24px; }
.dos-callout-warn { border: 1px solid var(--warn); background: var(--warn-soft); border-radius: var(--r-card); padding: 24px; }
.dos-callout-accent { border: 1px solid var(--accent-line); background: var(--accent-soft); border-radius: var(--r-card); padding: 24px; }
.dos-callout-label { font-size: 11.5px; font-weight: 600; letter-spacing: .16em; text-transform: uppercase; font-family: var(--display); margin-bottom: 8px; }

table.dos-table { width: 100%; border-collapse: collapse; font-size: 14px; min-width: 520px; }
table.dos-table th { position: sticky; top: 0; background: var(--surface); text-align: left; font-family: var(--display); font-weight: 600; padding: 16px 16px; border-bottom: 1px solid var(--border); white-space: nowrap; }
table.dos-table td { padding: 16px 16px; border-bottom: 1px solid var(--border); vertical-align: top; line-height: 1.5; }
/* table rows are pure data display, never a click target — no hover state. */
.dos-table-wrap { border: 1px solid var(--card-brd); border-radius: var(--r-card); overflow: auto; background: var(--card-bg); box-shadow: var(--shadow1); }

/* ---------- flashcards ---------- */
.dos-flip-card { width: 100%; min-height: 260px; background: var(--card-bg); border: 1px solid var(--card-brd); border-radius: 16px; padding: 32px; display: flex; align-items: center; justify-content: center; text-align: center; cursor: pointer; box-shadow: var(--shadow1); transition: transform .28s cubic-bezier(.2,.9,.3,1), box-shadow .28s, border-color .2s; }
.dos-flip-card:hover { transform: translateY(-3px); box-shadow: var(--shadow-lift); border-color: var(--accent-line); }
.dos-grade-grid { display: grid; grid-template-columns: repeat(4,1fr); gap: 8px; width: 100%; }
.dos-grade-grid button { min-height: 48px; border-radius: var(--r-btn); background: var(--card-bg); font-family: var(--display); font-size: 13px; font-weight: 600; cursor: pointer; border: 1px solid; transition: transform .18s cubic-bezier(.2,.9,.3,1), box-shadow .2s; }
.dos-grade-grid button:hover { transform: translateY(-2px); box-shadow: var(--shadow1); }

/* ---------- misc ---------- */
.dos-modal-scrim { position: fixed; inset: 0; z-index: 40; background: rgba(6,8,12,.5); -webkit-backdrop-filter: blur(4px); backdrop-filter: blur(4px); }
.dos-search-scrim { position: fixed; inset: 0; z-index: 50; background: rgba(6,8,12,.55); -webkit-backdrop-filter: blur(8px); backdrop-filter: blur(8px); display: flex; justify-content: center; align-items: flex-start; padding: 12vh 16px 16px; }
.dos-search-box { width: 100%; max-width: 560px; background: var(--glass); -webkit-backdrop-filter: var(--blur); backdrop-filter: var(--blur); border: 1px solid var(--glass-brd); border-radius: 16px; box-shadow: var(--shadow-lift); overflow: hidden; animation: dosPop .28s cubic-bezier(.16,.1,.3,1); }
.dos-mobilenav-scrim { position: fixed; inset: 0; z-index: 40; background: rgba(6,8,12,.55); -webkit-backdrop-filter: blur(8px); backdrop-filter: blur(8px); display: flex; align-items: flex-end; }

/* ---------- interactive cursor (fine-pointer only; added by inline script) ---------- */
.dos-cursor-ring { position: fixed; top: 0; left: 0; width: 34px; height: 34px; border-radius: 50%; border: 1.5px solid rgba(68,94,134,.6); background: transparent; pointer-events: none; z-index: 9999; transform: translate(-50%,-50%); will-change: left, top, width, height; transition: width .25s cubic-bezier(.2,.9,.3,1), height .25s cubic-bezier(.2,.9,.3,1), opacity .3s, background .25s, border-color .25s; }
.dos-cursor-dot { position: fixed; top: 0; left: 0; width: 5px; height: 5px; border-radius: 50%; background: rgba(68,94,134,.85); pointer-events: none; z-index: 9999; transform: translate(-50%,-50%); transition: opacity .3s, transform .15s; }
.dos-cursor-ring.hover { width: 54px; height: 54px; background: rgba(68,94,134,.10); border-color: rgba(68,94,134,.8); }
.dos-cursor-ring.press { transform: translate(-50%,-50%) scale(.85); }
#dos-root.dark ~ .dos-cursor-ring, #dos-root.amoled ~ .dos-cursor-ring { border-color: rgba(157,176,214,.7); }
#dos-root.dark ~ .dos-cursor-ring.hover, #dos-root.amoled ~ .dos-cursor-ring.hover { background: rgba(157,176,214,.14); border-color: rgba(157,176,214,.9); }
#dos-root.dark ~ .dos-cursor-dot, #dos-root.amoled ~ .dos-cursor-dot { background: rgba(205,214,233,.9); }

@media print {
  #dos-root > *:not(main), .dos-header, [data-no-print="true"], .dos-cursor-ring, .dos-cursor-dot { display: none !important; }
  #dos-root::before { display: none !important; }
  body, html { background: #fff !important; }
}

@media (max-width: 920px) {
  .dos-sidebar { display: none; }
}
/* Phone: keep the header on one row without horizontal overflow */
@media (max-width: 720px) {
  .dos-header { padding: 0 16px; gap: 8px; }
  .dos-search-btn { min-width: 0; max-width: none; }
  .dos-kbd { display: none; }
  .dos-h1-lg { font-size: 34px; }
}

/* ---------- immersive intro (portal) ---------- */
body.ux-intro-lock { overflow: hidden; }
#ux-intro { position: fixed; inset: 0; z-index: 9500; display: flex; align-items: center; justify-content: center; overflow: hidden; opacity: 1; transform: scale(1); transition: opacity 1s ease, transform 1.2s cubic-bezier(.7,0,.25,1);
  background:
    radial-gradient(1200px 700px at 12% -8%, rgba(96,116,160,.22), transparent 58%),
    radial-gradient(1000px 620px at 100% 0%, rgba(78,96,140,.18), transparent 56%),
    radial-gradient(900px 760px at 90% 110%, rgba(140,120,180,.16), transparent 60%),
    linear-gradient(180deg, #090A0E 0%, #06070A 100%); }
#ux-intro.exit { opacity: 0; transform: scale(1.08); pointer-events: none; }
#ux-intro-canvas { position: absolute; inset: 0; width: 100%; height: 100%; display: block; }
.ux-intro-inner { position: relative; z-index: 2; text-align: center; padding: 24px; max-width: 900px; }
.ux-intro-inner::before { content: ''; position: absolute; left: 50%; top: 50%; transform: translate(-50%,-50%); width: 150%; height: 150%; z-index: -1; pointer-events: none; background: radial-gradient(closest-side, rgba(6,7,11,.72), rgba(6,7,11,.35) 55%, transparent 78%); }
.ux-intro-eyebrow { color: rgba(228,234,247,.85); font: 700 12.5px/1 'Inter', system-ui, sans-serif; letter-spacing: .34em; text-transform: uppercase; opacity: 0; transform: translateY(10px); animation: uxIn .9s ease forwards .1s; text-shadow: 0 1px 20px rgba(0,0,0,.5); }
.ux-intro-title { font: 700 clamp(58px, 13vw, 172px)/.92 'Inter', system-ui, sans-serif; letter-spacing: -.045em; color: #fff; margin: 24px 0 0; display: flex; justify-content: center; text-shadow: 0 4px 60px rgba(0,0,0,.55); }
.ux-intro-title span { display: inline-block; transform: translateY(115%) rotate(7deg); opacity: 0; animation: uxLetter 1s cubic-bezier(.16,.9,.3,1) forwards; animation-delay: calc(.28s + var(--i) * .06s); }
.ux-intro-tag { color: rgba(234,239,250,.94); font: 450 clamp(16px, 2.4vw, 22px)/1.5 'Inter', system-ui, sans-serif; margin-top: 24px; opacity: 0; transform: translateY(12px); animation: uxIn 1s ease forwards .95s; text-shadow: 0 2px 24px rgba(0,0,0,.5); }
.ux-intro-enter { margin-top: 40px; height: 54px; padding: 0 32px; border-radius: 16px; border: 1px solid rgba(255,255,255,.22); background: rgba(255,255,255,.06); color: #fff; font: 600 15px 'Inter', system-ui, sans-serif; cursor: pointer; -webkit-backdrop-filter: blur(12px); backdrop-filter: blur(12px); display: inline-flex; align-items: center; gap: 8px; opacity: 0; transform: translateY(12px); animation: uxIn 1s ease forwards 1.15s; transition: background .25s, transform .25s, border-color .25s, box-shadow .25s; }
.ux-intro-enter span { transition: transform .3s cubic-bezier(.2,.9,.3,1); }
.ux-intro-enter:hover { background: rgba(255,255,255,.14); border-color: rgba(255,255,255,.42); transform: translateY(-2px); box-shadow: 0 16px 40px -16px rgba(120,140,190,.6); }
.ux-intro-enter:hover span { transform: translateX(5px); }
.ux-intro-hint { margin-top: 16px; color: rgba(208,216,234,.62); font: 600 11px 'Inter', system-ui, sans-serif; letter-spacing: .2em; text-transform: uppercase; opacity: 0; animation: uxIn 1s ease forwards 1.45s; }
@keyframes uxIn { to { opacity: 1; transform: none; } }
@keyframes uxLetter { to { transform: translateY(0) rotate(0); opacity: 1; } }
@media (prefers-reduced-motion: reduce) {
  #ux-intro, #ux-intro * { animation: none !important; opacity: 1 !important; transform: none !important; }
  #ux-intro { transition: opacity .4s ease !important; }
}
@media print { #ux-intro { display: none !important; } }

/* ---------- cinematic topic reader ---------- */
.dos-reader .dos-topic-progress { position: sticky; top: 66px; z-index: 12; height: 4px; margin: 0 0 4px; box-shadow: 0 6px 20px -10px rgba(0,0,0,.5); }
/* floating actions rail */
.dos-reader-rail { position: fixed; right: 26px; top: 50%; transform: translateY(-50%); z-index: 30; display: flex; flex-direction: column; gap: 8px; padding: 8px; border-radius: 16px; background: var(--glass); -webkit-backdrop-filter: var(--blur); backdrop-filter: var(--blur); border: 1px solid var(--glass-brd); box-shadow: var(--shadow-lift); animation: dosPop .45s cubic-bezier(.16,.9,.3,1); }
.dos-rail-btn { width: 42px; height: 42px; border-radius: 50%; border: 1px solid transparent; background: transparent; color: var(--ink2); cursor: pointer; display: flex; align-items: center; justify-content: center; transition: background .2s, color .2s, transform .2s cubic-bezier(.2,.9,.3,1); }
.dos-rail-btn:hover { background: var(--hover-soft); color: var(--hover-ink); transform: scale(1.12); }
.dos-rail-btn.is-on { background: var(--accent); color: var(--on-accent); border-color: var(--accent); }
@media (max-width: 1120px) { .dos-reader-rail { display: none; } }
/* reader content scroll-reveal (armed by fx.js) */
.dos-reader > .dos-reveal { opacity: 0; transform: translateY(26px); }
.dos-reader > .dos-reveal.dos-in { opacity: 1; transform: none; transition: opacity .7s cubic-bezier(.16,.9,.3,1), transform .8s cubic-bezier(.16,.9,.3,1); }
.dos-reader-head { position: relative; isolation: isolate; }
.dos-reader-head::before { content: ''; position: absolute; z-index: -1; left: -12%; top: -60%; width: 60%; height: 240%; pointer-events: none;
  background: radial-gradient(closest-side, var(--accent-soft), transparent 70%); opacity: .9; animation: dosReaderGlow 9s ease-in-out infinite alternate; }
@keyframes dosReaderGlow { 0% { transform: translate(0,0) scale(1); opacity: .55; } 100% { transform: translate(20%, 8%) scale(1.25); opacity: .95; } }
.dos-reader-title { animation: dosReaderTitle .85s cubic-bezier(.16,.9,.3,1) both; }
.dos-reader-head .dos-callout-label { animation: dosReaderTitle .7s cubic-bezier(.16,.9,.3,1) both; }
.dos-reader-head > p { animation: dosReaderTitle .95s cubic-bezier(.16,.9,.3,1) .08s both; }
@keyframes dosReaderTitle { 0% { opacity: 0; transform: translateY(26px); filter: blur(6px); } 100% { opacity: 1; transform: none; filter: blur(0); } }

/* ---------- dashboard "continue" hero ---------- */
.dos-continue { position: relative; overflow: hidden; display: flex; align-items: center; gap: 16px; width: 100%; padding: 24px 24px; border-radius: var(--r-card); border: 1px solid rgba(255,255,255,.12); cursor: pointer; color: #fff; text-align: left;
  background: radial-gradient(130% 160% at 0% 0%, rgba(157,176,214,.28), transparent 52%), linear-gradient(118deg, #262c42 0%, #191c28 55%, #131520 100%);
  box-shadow: var(--edge), var(--shadow-lift); transition: box-shadow .3s, border-color .3s; }
.dos-continue::after { content: ''; position: absolute; inset: 0; border-radius: inherit; pointer-events: none; opacity: 0; transition: opacity .35s ease; background: radial-gradient(520px circle at var(--mx,80%) var(--my,50%), var(--hover-glow), transparent 55%); }
.dos-continue.fx-tilt::after { opacity: 1; }
.dos-continue-ic { width: 46px; height: 46px; flex: none; border-radius: 8px; display: grid; place-items: center; background: rgba(255,255,255,.08); border: 1px solid rgba(255,255,255,.14); box-shadow: inset 0 1px 0 rgba(255,255,255,.14); }
.dos-continue-cta { flex: none; display: inline-flex; align-items: center; gap: 8px; height: 44px; padding: 0 24px; border-radius: 16px; background: #fff; color: #14161b; font-family: var(--display); font-weight: 600; font-size: 14px; box-shadow: 0 10px 24px -10px rgba(0,0,0,.6); }
.dos-continue:hover .dos-continue-cta span { transform: translateX(5px); }

/* ---------- chapter day card: lessons (read) vs practice (check) ---------- */
.dos-lesson-list { display: flex; flex-direction: column; gap: 8px; margin-top: 16px; }
.dos-lesson-row { display: flex; align-items: center; gap: 16px; width: 100%; text-align: left; padding: 16px 16px; border-radius: 8px; border: 1px solid var(--card-brd); background: var(--surface-alt); color: var(--ink); cursor: pointer; transition: border-color .2s, background .2s, transform .2s cubic-bezier(.2,.9,.3,1), box-shadow .2s; }
.dos-lesson-row:hover { border-color: var(--hover-line); background: var(--hover-soft); transform: translateX(4px); box-shadow: var(--shadow1); }
.dos-lesson-row:hover .dos-lesson-name { color: var(--hover-ink); }
.dos-lesson-row:hover .dos-lesson-go { color: var(--hover-ink); }
.dos-task-check:hover { background: var(--hover-soft); }
.dos-lesson-check { width: 22px; height: 22px; flex: none; border-radius: 50%; border: 1.5px solid var(--accent-line); display: flex; align-items: center; justify-content: center; font-size: 12px; color: var(--accent); transition: background .2s, border-color .2s; }
.dos-lesson-row.is-done .dos-lesson-check { background: var(--accent); color: var(--on-accent); border-color: var(--accent); }
.dos-lesson-name { flex: 1; font-size: 15px; font-weight: 500; }
.dos-lesson-row.is-done .dos-lesson-name { color: var(--ink2); }
/* Resting color is --ink2 at full opacity, not a dimmed accent — opacity blends
   toward the background and had fallen below WCAG AA contrast at rest. */
.dos-lesson-go { flex: none; font-size: 12.5px; font-weight: 600; color: var(--ink2); transition: color .2s, transform .2s cubic-bezier(.2,.9,.3,1); }
.dos-lesson-row:hover .dos-lesson-go { transform: translateX(3px); }
.dos-task-list { margin-top: 16px; border-top: 1px solid var(--card-brd); padding-top: 16px; display: flex; flex-direction: column; gap: 4px; }
.dos-task-check { display: flex; align-items: center; gap: 8px; padding: 4px 4px; font-size: 13.5px; line-height: 1.5; color: var(--ink2); cursor: pointer; border-radius: 8px; transition: background .15s; }
.dos-task-check input { width: 18px; height: 18px; flex: none; accent-color: var(--accent); cursor: pointer; }

/* ---------- chapters cards (clean, monochrome) ---------- */
.dos-chapter-card { position: relative; display: flex; flex-direction: column; text-align: left; cursor: pointer; color: var(--ink); background-color: var(--card-bg); background-image: linear-gradient(180deg, rgba(255,255,255,.035), rgba(255,255,255,0) 42%); border: 1px solid var(--card-brd); border-radius: 16px; padding: 24px; box-shadow: var(--edge), var(--shadow1); }
.dos-chapter-top { display: flex; align-items: center; justify-content: space-between; }
.dos-chapter-num { width: 46px; height: 46px; border-radius: 8px; display: flex; align-items: center; justify-content: center; font-family: var(--display); font-weight: 700; font-size: 18px; color: var(--ink); background: var(--surface-alt); border: 1px solid var(--card-brd); }
.dos-chapter-card.is-done .dos-chapter-num { background: var(--accent); color: var(--on-accent); border-color: var(--accent); }
.dos-chapter-ring { position: relative; width: 40px; height: 40px; display: grid; place-items: center; }
.dos-chapter-pct { position: absolute; font-size: 10.5px; font-weight: 700; color: var(--ink2); font-variant-numeric: tabular-nums; }
.dos-chapter-title { font-family: var(--serif); font-size: 21px; font-weight: 600; line-height: 1.25; margin-top: 4px; }
.dos-chapter-meta { font-size: 13.5px; color: var(--ink2); margin-top: 8px; }
.dos-chapter-foot { display: flex; align-items: center; justify-content: space-between; margin-top: auto; padding-top: 16px; margin-top: 16px; border-top: 1px solid var(--card-brd); font-size: 12.5px; font-weight: 500; color: var(--ink2); }
.dos-chapter-arrow { font-size: 17px; color: var(--ink2); transition: transform .3s cubic-bezier(.2,.9,.3,1), color .2s; }
.dos-chapter-card:hover .dos-chapter-arrow { color: var(--hover-ink); transform: translateX(4px); }

/* reader back button */
.dos-back-btn { display: inline-flex; align-items: center; gap: 8px; align-self: flex-start; height: 38px; padding: 0 16px 0 8px; border-radius: 16px; border: 1px solid var(--card-brd); background: var(--card-bg); color: var(--ink2); font-family: var(--display); font-size: 13.5px; font-weight: 600; cursor: pointer; box-shadow: var(--edge), var(--shadow1); transition: color .2s, border-color .2s, transform .2s cubic-bezier(.2,.9,.3,1), background .2s; }
.dos-back-btn:hover { color: var(--hover-ink); border-color: var(--hover-line); background: var(--hover-soft); transform: translateX(-3px); }

/* ---------- pinned chapter heading (scroll-driven feel) ---------- */
.dos-sticky-head { position: sticky; top: 66px; z-index: 11; padding: 16px 16px; margin: 0 -16px 4px; border-radius: 16px;
  background: var(--glass); -webkit-backdrop-filter: var(--blur); backdrop-filter: var(--blur); border: 1px solid var(--glass-brd); }
@media (prefers-reduced-motion: reduce) { .dos-reader-head::before, .dos-reader-title, .dos-reader-head > p, .dos-reader-head .dos-callout-label { animation: none !important; } }