/* Lecture Notebook — base + shared components. Logical properties only (RTL-first). */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; text-size-adjust: 100%; }
body {
  margin: 0;
  min-height: 100dvh;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-ui);
  font-size: var(--fs-md);
  line-height: var(--lh);
  -webkit-font-smoothing: antialiased;
  caret-color: var(--primary);
}
img, svg { display: block; max-width: 100%; }
button, input, select, textarea { font: inherit; color: inherit; }
button { cursor: pointer; }
a { color: var(--primary); text-underline-offset: 3px; text-decoration-thickness: 1px; }
h1, h2, h3, h4 { margin: 0; line-height: 1.3; text-wrap: balance; font-weight: 600; }
p { margin: 0; }
[hidden] { display: none !important; }

::selection { background: var(--highlight); color: var(--ink); }
:focus-visible { outline: 2px solid var(--focus); outline-offset: 2px; border-radius: 4px; }
* { scrollbar-width: thin; scrollbar-color: var(--line-strong) transparent; }
*::-webkit-scrollbar { width: 10px; height: 10px; }
*::-webkit-scrollbar-thumb { background: var(--line-strong); border-radius: 10px; border: 3px solid transparent; background-clip: padding-box; }
.tnum { font-variant-numeric: tabular-nums; }
.sr-only { position: absolute !important; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; border: 0; }

/* ---- notebook materials ---------------------------------------------- */
.nb-grid {
  background-color: var(--paper);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: var(--grid-size) var(--grid-size);
  background-position: -1px -1px;
}
/* red margin rule on the inline-start side of a writing area */
.nb-margin { position: relative; }
.nb-margin::before {
  content: "";
  position: absolute;
  inset-block: 0;
  inset-inline-start: 38px;
  width: 1.5px;
  background: var(--margin);
  opacity: 0.55;
  pointer-events: none;
}

/* ---- buttons --------------------------------------------------------- */
.btn {
  --b-bg: var(--paper);
  --b-fg: var(--ink);
  --b-bd: var(--line-strong);
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  min-height: 40px;
  padding: 0 16px;
  border: 1px solid var(--b-bd);
  border-radius: var(--r-md);
  background: var(--b-bg);
  color: var(--b-fg);
  font-size: var(--fs-md);
  font-weight: 500;
  line-height: 1;
  white-space: nowrap;
  text-decoration: none;
  transition: background var(--t-fast) var(--ease-out), border-color var(--t-fast) var(--ease-out), transform var(--t-fast) var(--ease-out), box-shadow var(--t-fast) var(--ease-out);
  -webkit-tap-highlight-color: transparent;
}
.btn:hover { background: var(--paper-2); }
.btn:active { transform: translateY(1px); }
.btn[disabled], .btn[aria-disabled="true"] { opacity: 0.45; pointer-events: none; }
.btn svg { width: 18px; height: 18px; flex: none; }
.btn-primary { --b-bg: var(--primary); --b-fg: var(--primary-ink); --b-bd: transparent; box-shadow: var(--shadow-tab); }
.btn-primary:hover { background: color-mix(in srgb, var(--primary) 88%, var(--ink)); }
.btn-ghost { --b-bg: transparent; --b-bd: transparent; }
.btn-ghost:hover { background: var(--paper-3); }
.btn-danger { --b-fg: var(--bad); }
.btn-danger:hover { background: var(--bad-soft); }
.btn-sm { min-height: 32px; padding: 0 12px; font-size: var(--fs-sm); border-radius: var(--r-sm); }
.btn-lg { min-height: 48px; padding: 0 22px; font-size: var(--fs-lg); }
.btn-icon { padding: 0; width: 40px; }
.btn-icon.btn-sm { width: 32px; }
.btn-block { width: 100%; }
.btn.is-busy { position: relative; color: transparent !important; pointer-events: none; }
.btn.is-busy::after {
  content: ""; position: absolute; width: 18px; height: 18px; border-radius: 50%;
  border: 2px solid var(--b-fg); border-inline-end-color: transparent;
  animation: spin 0.7s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* ---- fields ---------------------------------------------------------- */
.field { display: grid; gap: 6px; }
.field > label, .label { font-size: var(--fs-sm); font-weight: 500; color: var(--ink-2); }
.hint { font-size: var(--fs-xs); color: var(--ink-3); }
.input, .textarea, .select {
  width: 100%;
  min-height: 42px;
  padding: 9px 12px;
  border: 1px solid var(--line-strong);
  border-radius: var(--r-sm);
  background: var(--paper);
  color: var(--ink);
  font-size: var(--fs-md);
  line-height: 1.5;
  transition: border-color var(--t-fast) var(--ease-out), box-shadow var(--t-fast) var(--ease-out);
}
.input::placeholder, .textarea::placeholder { color: var(--ink-3); opacity: 1; }
.input:hover, .textarea:hover, .select:hover { border-color: var(--ink-3); }
.input:focus, .textarea:focus, .select:focus { outline: none; border-color: var(--primary); box-shadow: 0 0 0 3px color-mix(in srgb, var(--primary) 22%, transparent); }
.input[aria-invalid="true"] { border-color: var(--bad); }
.textarea { resize: vertical; min-height: 96px; }
.select { appearance: none; background-image: linear-gradient(45deg, transparent 50%, var(--ink-3) 50%), linear-gradient(135deg, var(--ink-3) 50%, transparent 50%); background-size: 5px 5px; background-repeat: no-repeat; background-position: left 16px center, left 11px center; padding-inline-start: 12px; padding-inline-end: 32px; }
/* the chevron sits at the inline-end in both directions; only its position flips */
[dir="ltr"] .select { background-position: right 11px center, right 16px center; }
.input-ltr { direction: ltr; text-align: start; }
[dir="rtl"] .input-ltr { text-align: right; }
.check { display: flex; align-items: flex-start; gap: 10px; font-size: var(--fs-sm); color: var(--ink-2); cursor: pointer; }
.check input { width: 18px; height: 18px; margin: 2px 0 0; accent-color: var(--primary); flex: none; }
.err { color: var(--bad); font-size: var(--fs-sm); }

/* segmented control */
.seg { display: inline-flex; padding: 3px; gap: 2px; border-radius: var(--r-md); background: var(--paper-2); border: 1px solid var(--line); }
.seg button { border: 0; background: transparent; padding: 6px 12px; border-radius: 7px; font-size: var(--fs-sm); color: var(--ink-2); display: inline-flex; gap: 6px; align-items: center; }
.seg button[aria-pressed="true"] { background: var(--paper); color: var(--ink); box-shadow: var(--shadow-tab); }
.seg svg { width: 16px; height: 16px; }

/* range slider */
.range { width: 100%; accent-color: var(--primary); }

/* ---- index tabs (vertical rail on the inline-start edge) -------------- */
.tabs-rail { display: flex; flex-direction: column; gap: 6px; padding-block: 12px; }
.tab {
  --tab: var(--violet); --tab-ink: var(--violet-ink);
  position: relative;
  display: grid; justify-items: center; gap: 3px;
  width: 64px; padding: 10px 4px 9px;
  border: 0;
  background: var(--tab-rest, var(--paper-2)); /* divider tabs are coloured stock even when not selected */
  color: var(--ink-2);
  font-size: 11.5px; font-weight: 500; line-height: 1.2; text-align: center;
  box-shadow: var(--shadow-tab);
  transition: transform var(--t-med) var(--ease-out), background var(--t-fast), color var(--t-fast);
}
/* rail sits on the inline-start edge: the free (rounded) end faces outward */
[dir="rtl"] .tab { border-radius: 0 var(--r-md) var(--r-md) 0; }
[dir="ltr"] .tab { border-radius: var(--r-md) 0 0 var(--r-md); }
.tab::before { /* the coloured tab edge — the index tab itself */
  content: ""; position: absolute; inset-block: 6px; inset-inline-start: 0; width: 4px;
  border-radius: 2px; background: var(--tab); opacity: 0.55;
}
.tab svg { width: 20px; height: 20px; }
.tab:hover { color: var(--ink); background: color-mix(in srgb, var(--tab) 22%, var(--paper-2)); }
.tab[aria-selected="true"] { background: var(--tab); color: var(--tab-ink); transform: translateX(var(--pull, 4px)); }
[dir="ltr"] .tab[aria-selected="true"] { transform: translateX(calc(var(--pull, 4px) * -1)); }
.tab[aria-selected="true"]::before { opacity: 0; }
.tab.t-violet { --tab: var(--violet); --tab-ink: var(--violet-ink); --tab-rest: var(--violet-soft); }
.tab.t-teal { --tab: var(--teal); --tab-ink: var(--teal-ink); --tab-rest: var(--teal-soft); }
.tab.t-amber { --tab: var(--amber); --tab-ink: var(--amber-ink); --tab-rest: var(--amber-soft); }
.tab.t-coral { --tab: var(--coral); --tab-ink: var(--coral-ink); --tab-rest: var(--coral-soft); }
.tab.t-blue { --tab: var(--blue); --tab-ink: var(--blue-ink); --tab-rest: var(--blue-soft); }
.tab .dot { position: absolute; inset-block-start: 6px; inset-inline-end: 6px; width: 7px; height: 7px; border-radius: 50%; background: var(--coral); }

/* horizontal tab bar (mobile bottom bar reuses .tab with .tab-h) */
.tab-h { width: auto; flex: 1; border-radius: var(--r-md) var(--r-md) 0 0 !important; transform: none !important; }
.tab-h::before { inset-block: auto 0; inset-inline: 10px; width: auto; height: 3px; }

/* ---- stamps: state is line form + label, never colour alone ------------ */
.stamp {
  --s: var(--ink-3);
  display: inline-flex; align-items: center; gap: 5px;
  padding: 2px 8px;
  border: 1.5px dashed var(--s);
  border-radius: 6px;
  color: var(--s);
  font-size: 11.5px; font-weight: 600; line-height: 1.5;
  transform: rotate(-2.5deg);
  white-space: nowrap;
}
.stamp svg { width: 13px; height: 13px; }
.stamp.is-done { border-style: solid; }
.stamp.is-void { border-style: solid; text-decoration: line-through; opacity: 0.7; }
.stamp.s-ok { --s: var(--ok); }
.stamp.s-violet { --s: var(--violet); }
.stamp.s-teal { --s: var(--teal-text); }
.stamp.s-warn { --s: var(--warn); }
.stamp.s-bad { --s: var(--bad); }
.stamp.press { animation: stamp-press var(--t-slow) var(--ease-out) both; }
@keyframes stamp-press {
  0% { transform: scale(1.35) rotate(-9deg); opacity: 0; }
  60% { transform: scale(0.95) rotate(-2deg); opacity: 1; }
  100% { transform: scale(1) rotate(-2.5deg); }
}

/* ---- the highlighter: text the AI wrote --------------------------------- */
.hl {
  background-image: linear-gradient(transparent 55%, var(--highlight) 55%, var(--highlight) 90%, transparent 90%);
  background-repeat: no-repeat;
  background-size: 100% 100%;
  background-position: right center;
  -webkit-box-decoration-break: clone; box-decoration-break: clone;
}
[dir="ltr"] .hl { background-position: left center; }
.hl.sweep { animation: hl-sweep 520ms var(--ease-out) both; }
@keyframes hl-sweep { from { background-size: 0% 100%; } to { background-size: 100% 100%; } }

/* ---- chips ------------------------------------------------------------- */
.chip {
  display: inline-flex; align-items: center; gap: 6px;
  min-height: 30px; padding: 3px 10px;
  border: 1px solid var(--line-strong); border-radius: 999px;
  background: var(--paper); color: var(--ink-2);
  font-size: var(--fs-sm);
}
button.chip:hover { border-color: var(--primary); color: var(--ink); }
.chip svg { width: 14px; height: 14px; }
.chip .x { border: 0; background: none; padding: 0; color: var(--ink-3); display: inline-grid; }
.chip .x:hover { color: var(--bad); }

/* ---- page chrome ---------------------------------------------------------- */
.topbar {
  position: sticky; top: 0; z-index: 30;
  display: flex; align-items: center; gap: var(--gap-3);
  min-height: 60px; padding: 8px 16px;
  background: color-mix(in srgb, var(--paper) 92%, transparent);
  backdrop-filter: saturate(1.4) blur(10px);
  border-bottom: 1px solid var(--line);
}
.topbar .spacer { flex: 1; }
.brand { display: inline-flex; align-items: center; gap: 10px; color: var(--ink); text-decoration: none; font-weight: 600; font-size: var(--fs-md); }
.brand img { width: 32px; height: 32px; border-radius: 8px; }
.brand small { display: block; font-weight: 400; font-size: 11.5px; color: var(--ink-3); line-height: 1.2; }
.beta { font-size: 11px; font-weight: 600; color: var(--violet); border: 1.5px solid currentColor; border-radius: 5px; padding: 0 6px; transform: rotate(-3deg); display: inline-block; }

/* ---- surfaces ----------------------------------------------------------- */
.sheet-card { background: var(--paper); border: 1px solid var(--line); border-radius: var(--r-lg); }
.muted { color: var(--ink-3); }
.row { display: flex; align-items: center; gap: var(--gap-2); }
.stack { display: grid; gap: var(--gap-3); }
.divider { height: 1px; background: var(--line); border: 0; margin: var(--gap-4) 0; }

/* ---- dialog -------------------------------------------------------------- */
dialog.dlg {
  width: min(520px, calc(100vw - 24px));
  max-height: calc(100dvh - 32px);
  padding: 0;
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  background: var(--paper);
  color: var(--ink);
  box-shadow: var(--shadow-pop);
}
dialog.dlg::backdrop { background: rgba(13, 14, 18, 0.45); backdrop-filter: blur(2px); }
dialog.dlg[open] { animation: dlg-in var(--t-med) var(--ease-out); }
@keyframes dlg-in { from { opacity: 0; transform: translateY(10px) scale(0.98); } }
.dlg-head { display: flex; align-items: center; gap: 10px; padding: 18px 20px 6px; }
.dlg-head h2 { font-size: var(--fs-xl); flex: 1; }
.dlg-body { padding: 8px 20px 18px; display: grid; gap: var(--gap-4); overflow: auto; }
.dlg-foot { display: flex; gap: 8px; justify-content: flex-end; padding: 14px 20px; border-top: 1px solid var(--line); background: var(--paper-2); border-radius: 0 0 var(--r-lg) var(--r-lg); flex-wrap: wrap; }

/* ---- toasts -------------------------------------------------------------- */
.toasts { position: fixed; z-index: 100; inset-inline: 0; bottom: 20px; display: grid; justify-items: center; gap: 8px; pointer-events: none; padding: 0 12px; }
.toast {
  pointer-events: auto;
  display: flex; align-items: center; gap: 10px;
  max-width: min(520px, 100%);
  padding: 10px 14px;
  border-radius: var(--r-md);
  background: var(--ink); color: var(--ink-inverse);
  box-shadow: var(--shadow-pop);
  font-size: var(--fs-sm);
  animation: toast-in var(--t-med) var(--ease-out);
}
.toast svg { width: 18px; height: 18px; flex: none; }
.toast.t-bad { background: var(--bad); color: var(--ink-inverse); } /* white on red (light), dark ink on pink (dark): both >= 5.5:1 */
.toast.t-ok svg { color: var(--ok); }
@keyframes toast-in { from { opacity: 0; transform: translateY(8px); } }

/* ---- menus --------------------------------------------------------------- */
.menu { position: fixed; z-index: 60; min-width: 200px; padding: 6px; border: 1px solid var(--line); border-radius: var(--r-md); background: var(--paper); box-shadow: var(--shadow-pop); }
.menu button { display: flex; width: 100%; align-items: center; gap: 10px; padding: 9px 10px; border: 0; background: none; border-radius: 7px; font-size: var(--fs-sm); color: var(--ink); text-align: start; }
.menu button:hover { background: var(--paper-2); }
.menu button.danger { color: var(--bad); }
.menu svg { width: 17px; height: 17px; color: var(--ink-3); }

/* ---- empty + loading states --------------------------------------------- */
.empty { display: grid; justify-items: center; gap: 10px; text-align: center; padding: 40px 20px; color: var(--ink-3); }
.empty svg { width: 36px; height: 36px; color: var(--ink-3); }
.skeleton { background: linear-gradient(90deg, var(--paper-2), var(--paper-3), var(--paper-2)); background-size: 200% 100%; animation: sk 1.2s linear infinite; border-radius: var(--r-sm); }
@keyframes sk { to { background-position: -200% 0; } }
.boot { min-height: 100dvh; display: grid; place-items: center; }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 1ms !important; animation-iteration-count: 1 !important; transition-duration: 1ms !important; }
}

/* direction-sensitive icons point the reading way */
[dir="rtl"] .flip-rtl { transform: scaleX(-1); }

/* iOS Safari and in-app WebViews zoom into any field under 16px on focus */
@media (pointer: coarse) {
  .input, .textarea, .select { font-size: max(16px, var(--fs-md)); }
}
.ic { width: 20px; height: 20px; flex: none; }