/* Study site: soft dark by default, light optional. */
:root {
  --bg: #1f2128;
  --panel: #272a33;
  --panel-2: #2f333d;
  --border: #3a3f4b;
  --text: #e4e4e7;
  --muted: #9a9ca6;
  --accent: #7aa2f7;
  --accent-text: #1a1c22;
  --good: #73c48f;
  --bad: #ef7f8a;
  --warn: #e3b36a;
  --radius: 10px;
  --mono: ui-monospace, "Cascadia Code", "JetBrains Mono", Consolas, monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --ai-w: 420px;
  color-scheme: dark;
}
:root[data-theme="light"] {
  --bg: #f6f6f4;
  --panel: #ffffff;
  --panel-2: #f0f0ee;
  --border: #dddcd7;
  --text: #24262b;
  --muted: #6c6e76;
  --accent: #3b6fd8;
  --accent-text: #ffffff;
  --good: #2f8a50;
  --bad: #c9414f;
  --warn: #a8701c;
  color-scheme: light;
}

* { box-sizing: border-box; }
html, body { margin: 0; background: var(--bg); color: var(--text); font: 15px/1.55 var(--sans); }
body { min-height: 100vh; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
h1, h2, h3 { line-height: 1.25; margin: 0 0 .6em; font-weight: 600; }
h1 { font-size: 1.45rem; }
h2 { font-size: 1.15rem; }
h3 { font-size: 1rem; }
code, pre, kbd { font-family: var(--mono); font-size: .9em; }
hr { border: 0; border-top: 1px solid var(--border); margin: 1.2rem 0; }
::selection { background: color-mix(in srgb, var(--accent) 35%, transparent); }

/* layout */
.top {
  position: sticky; top: 0; z-index: 20; display: flex; align-items: center; gap: .25rem;
  padding: .5rem 1rem; background: color-mix(in srgb, var(--bg) 92%, transparent);
  backdrop-filter: blur(6px); border-bottom: 1px solid var(--border);
}
.top .brand { font-weight: 700; color: var(--text); margin-right: .75rem; display: flex; align-items: center; gap: .45rem; }
.top .brand img { width: 22px; height: 22px; }
.top a.nav { color: var(--muted); padding: .35rem .6rem; border-radius: 8px; }
.top a.nav:hover, .top a.nav.on { color: var(--text); background: var(--panel); text-decoration: none; }
.top .spacer { flex: 1; }
.wrap { display: flex; }
main { flex: 1; min-width: 0; padding: 1.25rem 1rem 4rem; }
.page { max-width: 980px; margin: 0 auto; }
.page.narrow { max-width: 760px; }
.page.wide { max-width: 1400px; }
body.ai-open main { margin-right: var(--ai-w); }

/* generic bits */
.card { background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius); padding: 1rem 1.1rem; }
.card + .card { margin-top: .8rem; }
.muted { color: var(--muted); }
.small { font-size: .86rem; }
.row { display: flex; align-items: center; gap: .5rem; flex-wrap: wrap; }
.row.between { justify-content: space-between; }
.stack > * + * { margin-top: .8rem; }
.grid { display: grid; gap: .8rem; grid-template-columns: repeat(auto-fill, minmax(270px, 1fr)); }
.right { margin-left: auto; }
.center { text-align: center; }
.hidden { display: none !important; }
.err { color: var(--bad); }
.ok { color: var(--good); }

button, .btn {
  font: inherit; color: var(--text); background: var(--panel-2); border: 1px solid var(--border);
  border-radius: 8px; padding: .4rem .8rem; cursor: pointer; display: inline-flex; align-items: center; gap: .35rem;
  text-decoration: none; white-space: nowrap;
}
button:hover, .btn:hover { border-color: color-mix(in srgb, var(--accent) 50%, var(--border)); text-decoration: none; }
button:disabled { opacity: .5; cursor: default; }
button.primary, .btn.primary { background: var(--accent); color: var(--accent-text); border-color: var(--accent); font-weight: 600; }
button.ghost { background: transparent; border-color: transparent; color: var(--muted); }
button.ghost:hover { color: var(--text); background: var(--panel-2); }
button.good { border-color: var(--good); color: var(--good); }
button.bad { border-color: var(--bad); color: var(--bad); }
button.warn { border-color: var(--warn); color: var(--warn); }
button.sm { padding: .2rem .55rem; font-size: .85rem; }
button.on { background: color-mix(in srgb, var(--accent) 22%, var(--panel-2)); border-color: var(--accent); }

input, textarea, select {
  font: inherit; color: var(--text); background: var(--bg); border: 1px solid var(--border); border-radius: 8px;
  padding: .45rem .6rem; width: 100%;
}
input:focus, textarea:focus, select:focus, button:focus-visible { outline: 2px solid color-mix(in srgb, var(--accent) 60%, transparent); outline-offset: 1px; }
input[type=checkbox], input[type=radio] { width: auto; accent-color: var(--accent); }
textarea { resize: vertical; min-height: 5rem; }
textarea.code { font-family: var(--mono); font-size: .85rem; min-height: 14rem; white-space: pre; }
label.field { display: block; margin-bottom: .7rem; }
label.field > span { display: block; color: var(--muted); font-size: .85rem; margin-bottom: .2rem; }

.chip {
  display: inline-flex; align-items: center; gap: .3rem; padding: .18rem .6rem; border-radius: 999px;
  border: 1px solid var(--border); background: var(--panel); color: var(--muted); font-size: .85rem; cursor: pointer;
}
.chip.on { color: var(--text); border-color: var(--accent); background: color-mix(in srgb, var(--accent) 16%, var(--panel)); }
.chip:hover { color: var(--text); }
.tag { display: inline-block; padding: .05rem .45rem; border-radius: 6px; background: var(--panel-2); color: var(--muted); font-size: .78rem; }
.tag.exam { color: var(--warn); }
.dot { display: inline-block; width: .6rem; height: .6rem; border-radius: 50%; background: var(--border); flex: none; }
.dot.correct { background: var(--good); }
.dot.partial { background: var(--warn); }
.dot.wrong { background: var(--bad); }
.who { display: inline-flex; align-items: center; justify-content: center; width: 1.25rem; height: 1.25rem; border-radius: 50%;
  font-size: .68rem; font-weight: 700; color: #1a1c22; opacity: .35; }
.who.correct, .who.partial, .who.wrong { opacity: 1; }
.who.wrong { outline: 2px solid var(--bad); }
.who.partial { outline: 2px solid var(--warn); }
.bar { height: 5px; border-radius: 3px; background: var(--panel-2); overflow: hidden; }
.bar > i { display: block; height: 100%; background: var(--good); }

.tabs { display: flex; gap: .2rem; border-bottom: 1px solid var(--border); margin: 1rem 0; overflow-x: auto; overflow-y: hidden; scrollbar-width: none; }
.tabs a { padding: .45rem .8rem; color: var(--muted); border-bottom: 2px solid transparent; margin-bottom: -1px; white-space: nowrap; }
.tabs a.on { color: var(--text); border-color: var(--accent); }
.tabs a:hover { text-decoration: none; color: var(--text); }

.list { display: flex; flex-direction: column; }
.item {
  display: flex; gap: .7rem; align-items: flex-start; padding: .7rem .8rem; border: 1px solid var(--border); border-radius: var(--radius);
  background: var(--panel); color: var(--text); margin-bottom: .45rem;
}
a.item:hover { text-decoration: none; border-color: color-mix(in srgb, var(--accent) 45%, var(--border)); }
.item .grow { flex: 1; min-width: 0; }
.item .title { font-weight: 600; }
.item.dim { opacity: .45; }
.clamp { display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }
.freq { font-variant-numeric: tabular-nums; min-width: 2.2rem; text-align: center; font-weight: 700; color: var(--warn); font-size: 1.05rem; }
.freq small { display: block; font-weight: 400; font-size: .68rem; color: var(--muted); }

table { border-collapse: collapse; width: 100%; }
th, td { padding: .4rem .55rem; border-bottom: 1px solid var(--border); text-align: left; vertical-align: top; }
th { color: var(--muted); font-weight: 500; font-size: .85rem; }

/* markdown */
.md > :first-child { margin-top: 0; }
.md > :last-child { margin-bottom: 0; }
.md p { margin: .55em 0; }
.md ul, .md ol { padding-left: 1.4em; margin: .5em 0; }
.md pre { background: var(--bg); border: 1px solid var(--border); border-radius: 8px; padding: .7rem .8rem; overflow-x: auto; position: relative; }
.md :not(pre) > code { background: var(--panel-2); padding: .05em .35em; border-radius: 5px; }
.md table { margin: .6em 0; display: block; overflow-x: auto; }
.md blockquote { margin: .6em 0; padding: .1em .9em; border-left: 3px solid var(--border); color: var(--muted); }
.md img { max-width: 100%; }
.md .katex-display { overflow-x: auto; overflow-y: hidden; padding: .2em 0; }
.md pre .copy { position: absolute; top: .35rem; right: .35rem; opacity: 0; }
.md pre:hover .copy { opacity: 1; }

/* login */
.login { max-width: 360px; margin: 12vh auto; }
.login h1 { text-align: center; margin-bottom: 1.2rem; }

/* course */
.course-card { display: flex; flex-direction: column; gap: .5rem; color: var(--text); }
.course-card:hover { text-decoration: none; border-color: color-mix(in srgb, var(--accent) 45%, var(--border)); }
.course-card .code { font-weight: 700; }
.countdown { color: var(--warn); font-size: .86rem; }
.exam-chips { display: flex; gap: .4rem; flex-wrap: wrap; align-items: center; }
.topic-pick { max-height: 50vh; overflow: auto; border: 1px solid var(--border); border-radius: 8px; padding: .3rem; }
.topic-pick label { display: flex; gap: .5rem; padding: .25rem .4rem; border-radius: 6px; cursor: pointer; user-select: none; }
.topic-pick label:hover { background: var(--panel-2); }

/* question */
.q-head { display: flex; flex-wrap: wrap; gap: .4rem; align-items: center; margin-bottom: .6rem; }
.q-prompt { font-size: 1.02rem; }
.options { display: flex; flex-direction: column; gap: .4rem; margin: .8rem 0; }
.option { display: flex; gap: .6rem; align-items: flex-start; text-align: left; padding: .55rem .75rem; white-space: normal; width: 100%; }
.option .letter { font-weight: 700; color: var(--muted); min-width: 1.1rem; }
.option.sel { border-color: var(--accent); }
.option.right { border-color: var(--good); background: color-mix(in srgb, var(--good) 12%, var(--panel-2)); }
.option.wrongpick { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 12%, var(--panel-2)); }
.steps { counter-reset: s; padding: 0; margin: .5rem 0; list-style: none; }
.steps li { counter-increment: s; position: relative; padding: .55rem .7rem .55rem 2.4rem; border: 1px solid var(--border); border-radius: 8px; margin-bottom: .4rem; background: var(--panel); }
.steps li::before { content: counter(s); position: absolute; left: .7rem; top: .55rem; color: var(--muted); font-weight: 700; }
.result { padding: .6rem .8rem; border-radius: 8px; border: 1px solid var(--border); }
.result.good { border-color: var(--good); }
.result.bad { border-color: var(--bad); }
.result.partial { border-color: var(--warn); }
.answer-box { border: 1px solid var(--border); border-radius: 8px; background: var(--bg); }
math-field { display: block; width: 100%; min-height: 3rem; padding: .4rem .6rem; font-size: 1.15rem; background: var(--bg);
  color: var(--text); border: 1px solid var(--border); border-radius: 8px; --caret-color: var(--accent);
  --selection-background-color: color-mix(in srgb, var(--accent) 30%, transparent); --contains-highlight-background-color: transparent; }
math-field::part(virtual-keyboard-toggle), math-field::part(menu-toggle) { color: var(--muted); }
.lines { display: flex; flex-direction: column; gap: .35rem; }
.lines .line { display: flex; gap: .35rem; align-items: center; }
.lines .line math-field { flex: 1; }
.photo-thumb { max-height: 160px; border-radius: 8px; border: 1px solid var(--border); }
.sticky-actions { position: sticky; bottom: 0; background: linear-gradient(transparent, var(--bg) 30%); padding: 1rem 0 .4rem; }

/* code */
.editor { height: 420px; border: 1px solid var(--border); border-radius: 8px; overflow: hidden; }
.editor.tall { height: 60vh; }
.out { font-family: var(--mono); font-size: .84rem; white-space: pre-wrap; background: var(--bg); border: 1px solid var(--border);
  border-radius: 8px; padding: .6rem .7rem; max-height: 340px; overflow: auto; margin: 0; }
.out.err { color: var(--bad); }
.test { border: 1px solid var(--border); border-radius: 8px; padding: .5rem .7rem; margin-bottom: .4rem; }
.test.pass { border-color: var(--good); }
.test.fail { border-color: var(--bad); }
.test .cols { display: grid; grid-template-columns: repeat(auto-fit, minmax(180px, 1fr)); gap: .5rem; }

/* AI panel */
.ai {
  position: fixed; top: 0; right: 0; bottom: 0; width: var(--ai-w); z-index: 30; display: flex; flex-direction: column;
  background: var(--panel); border-left: 1px solid var(--border);
}
.ai-head { display: flex; align-items: center; gap: .3rem; padding: .55rem .7rem; border-bottom: 1px solid var(--border); }
.ai-head .title { font-weight: 600; flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.ai-msgs { flex: 1; overflow-y: auto; padding: .8rem; display: flex; flex-direction: column; gap: .7rem; }
.msg { max-width: 100%; }
.msg.user { align-self: flex-end; background: color-mix(in srgb, var(--accent) 16%, var(--panel-2)); padding: .45rem .7rem; border-radius: 10px 10px 2px 10px; max-width: 88%; white-space: pre-wrap; }
.msg.assistant { line-height: 1.55; }
.msg img { max-width: 160px; border-radius: 6px; display: block; margin-top: .3rem; }
.msg .tool { color: var(--muted); font-size: .8rem; font-style: italic; }
.ai-ctx { font-size: .78rem; color: var(--muted); padding: .25rem .8rem; border-top: 1px solid var(--border); display: flex; gap: .4rem; align-items: center; }
.ai-input { padding: .55rem .7rem .7rem; border-top: 1px solid var(--border); }
.ai-input textarea { min-height: 2.6rem; max-height: 12rem; resize: none; }
.ai-input .row { margin-top: .4rem; }
.ai-thumbs { display: flex; gap: .3rem; margin-bottom: .3rem; }
.ai-thumbs img { height: 48px; border-radius: 6px; border: 1px solid var(--border); }
.ai-hist { padding: .5rem; overflow-y: auto; flex: 1; }
.ai-hist a { display: block; padding: .45rem .6rem; border-radius: 6px; color: var(--text); }
.ai-hist a:hover { background: var(--panel-2); text-decoration: none; }
.ai-fab { position: fixed; right: 1rem; bottom: 1rem; z-index: 25; border-radius: 999px; padding: .6rem 1rem; box-shadow: 0 4px 18px rgba(0,0,0,.3); }
.typing::after { content: "▍"; animation: blink 1s steps(2) infinite; color: var(--muted); }
@keyframes blink { 50% { opacity: 0; } }

/* modal + toast */
.modal-bg { position: fixed; inset: 0; background: rgba(0,0,0,.5); z-index: 50; display: flex; align-items: flex-start; justify-content: center; padding: 6vh 1rem; overflow-y: auto; }
.modal { background: var(--panel); border: 1px solid var(--border); border-radius: 12px; padding: 1.1rem 1.2rem; width: 100%; max-width: 560px; }
.modal.wide { max-width: 860px; }
.toast { position: fixed; bottom: 1.2rem; left: 50%; transform: translateX(-50%); z-index: 60; background: var(--panel-2);
  border: 1px solid var(--border); padding: .5rem 1rem; border-radius: 8px; box-shadow: 0 4px 16px rgba(0,0,0,.3); }
.toast.bad { border-color: var(--bad); }

/* tools */
.tool-frame { min-height: 60vh; }

@media (max-width: 900px) {
  :root { --ai-w: 100vw; }
  body.ai-open main { margin-right: 0; }
  .top a.nav span.lbl { display: none; }
}
@media (max-width: 600px) {
  main { padding: 1rem .75rem 4rem; }
  .grid { grid-template-columns: 1fr; }
  .editor { height: 340px; }
}

/* phone companion + QR */
.qr { background: #fff; border-radius: 10px; padding: .5rem; width: min(260px, 70vw); margin: .3rem auto .8rem; }
.qr svg { display: block; width: 100%; height: auto; }
.grow { flex: 1; min-width: 0; }
.phone { display: flex; flex-direction: column; min-height: 100dvh; max-width: 640px; margin: 0 auto; }
.phone-head { display: flex; align-items: center; gap: .5rem; padding: .6rem .8rem; border-bottom: 1px solid var(--border); position: sticky; top: 0; background: var(--bg); z-index: 5; }
.phone-q { margin: .6rem .8rem 0; max-height: 40vh; overflow-y: auto; }
.phone-feed { flex: 1; padding: .8rem; display: flex; flex-direction: column; gap: .7rem; }
.phone-feed .msg img { max-width: 46%; display: inline-block; margin: .3rem .3rem 0 0; }
.phone-bar { position: sticky; bottom: 0; background: var(--panel); border-top: 1px solid var(--border); padding: .6rem .8rem calc(.6rem + env(safe-area-inset-bottom)); display: flex; flex-direction: column; gap: .5rem; }
.phone-bar .row { flex-wrap: nowrap; gap: .5rem; }
.phone-bar button.big { padding: .8rem 1rem; font-size: 1.05rem; }
.phone-shots { display: flex; gap: .4rem; overflow-x: auto; }
.phone-shots .shot { position: relative; flex: none; }
.phone-shots img { height: 72px; border-radius: 6px; border: 1px solid var(--border); display: block; }
.phone-shots .shot button { position: absolute; top: 2px; right: 2px; padding: 0 .35rem; line-height: 1.4; }