:root {
  --bg: #f1f5fc;
  --panel: #ffffff;
  --ink: #142641;
  --muted: #5c6b80;
  --line: #dfe4ee;
  --brand: #142641;
  --accent: #245ce5;
  --accent-ink: #ffffff;
  --ok: #15803d;
  --ok-bg: #e8f6ed;
  --bad: #b42318;
  --bad-bg: #fdecea;
  --note-bg: #fff6e0;
  --radius: 10px;
}
:root { color-scheme: light; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    color-scheme: dark;
    --bg: #11151d; --panel: #1a2030; --ink: #e8ecf4; --muted: #9aa5ba; --line: #2b3347;
    --brand: #0c1830; --accent: #5b8dff; --accent-ink: #0b1220;
    --ok: #5fd08a; --ok-bg: #16301f; --bad: #ff8a80; --bad-bg: #3a1a18; --note-bg: #3a3014;
  }
}
:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #11151d; --panel: #1a2030; --ink: #e8ecf4; --muted: #9aa5ba; --line: #2b3347;
  --brand: #0c1830; --accent: #5b8dff; --accent-ink: #0b1220;
  --ok: #5fd08a; --ok-bg: #16301f; --bad: #ff8a80; --bad-bg: #3a1a18; --note-bg: #3a3014;
}
* { box-sizing: border-box; }
html { font-size: 16px; }
body { margin: 0; background: var(--bg); color: var(--ink); font-family: Inter, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif; line-height: 1.5; }
.loading { padding: 2rem; color: var(--muted); }
a { color: var(--accent); }
button { font: inherit; cursor: pointer; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }

/* top bar */
/* brand fonts: set here when white-labelling */
:root { --font-display: "Bodoni Moda", Georgia, serif; --font-tagline: "Cormorant Garamond", Georgia, serif; }
.topbar { background: var(--panel); color: var(--ink); border-bottom: 1px solid var(--line); display: flex; align-items: center; gap: 1rem; padding: 0.6rem 1rem; }
.topbar a { color: var(--ink); text-decoration: none; }
.brand { display: flex; align-items: center; gap: .5rem; }
.brand .wordmark { font-family: var(--font-display); font-size: 1.45rem; letter-spacing: -.5px; line-height: 1; }
.brand .product { font-size: .75rem; font-weight: 600; letter-spacing: .12em; text-transform: uppercase; color: var(--accent); margin-left: .15rem; }
.crown { width: 1.6rem; height: 1.6rem; fill: none; stroke: var(--accent); stroke-width: 1.5; stroke-linecap: round; stroke-linejoin: round; }
.crown.big { width: 2.6rem; height: 2.6rem; }
.auth-brand { text-align: center; margin-bottom: 1.2rem; }
.auth-brand .wordmark { font-family: var(--font-display); font-size: 2.6rem; letter-spacing: -1px; line-height: 1.1; }
.auth-brand .tagline { font-family: var(--font-tagline); font-style: italic; font-weight: 500; font-size: 1.3rem; color: var(--accent); }
.auth h1 { text-align: center; font-size: 1.1rem; }
.auth .sub { text-align: center; }
.crumb { color: var(--muted); border-left: 1px solid var(--line); padding-left: 1rem; }
.spacer { flex: 1; }
.who em { opacity: .75; font-style: normal; }
.link { background: none; border: 0; color: var(--accent); text-decoration: underline; padding: 0; }

/* layout */
.layout { display: grid; grid-template-columns: 310px 1fr; min-height: calc(100vh - 52px); }
.sidebar { background: var(--panel); border-right: 1px solid var(--line); padding: 1rem; overflow-y: auto; }
.main { padding: 1.5rem clamp(1rem, 3vw, 2.5rem); max-width: 60rem; width: 100%; }
@media (max-width: 800px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { border-right: 0; border-bottom: 1px solid var(--line); }
}

/* sidebar */
.side-title { font-weight: 700; margin: 0 0 .25rem; }
.side-sub { color: var(--muted); font-size: .85rem; margin-bottom: .75rem; }
.side-link { display: block; padding: .35rem .5rem; border-radius: 6px; text-decoration: none; color: var(--ink); }
.side-link:hover { background: var(--bg); }
.side-link.current { background: var(--accent); color: var(--accent-ink); }
details.chapter { margin: .4rem 0; }
details.chapter > summary { cursor: pointer; font-weight: 600; padding: .35rem .25rem; }
.sec { display: flex; justify-content: space-between; align-items: center; gap: .5rem; padding: .4rem .5rem .4rem 1rem; border-radius: 6px; text-decoration: none; color: var(--ink); font-size: .95rem; }
.sec:hover { background: var(--bg); }
.sec.current { background: var(--accent); color: var(--accent-ink); }
.sec .count { font-size: .8rem; opacity: .8; white-space: nowrap; }
.sec.done .count::before { content: "✔ "; color: var(--ok); }
.sec.current.done .count::before { color: var(--accent-ink); }

/* progress bar */
.bar { height: 8px; background: var(--line); border-radius: 99px; overflow: hidden; }
.bar > span { display: block; height: 100%; background: var(--ok); }

/* cards + headings */
h1 { font-size: 1.5rem; margin: 0 0 .25rem; }
.sub { color: var(--muted); margin: 0 0 1.25rem; }
.card { background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.1rem 1.25rem; margin-bottom: 1rem; }
.problem-head { display: flex; justify-content: space-between; gap: 1rem; align-items: baseline; margin-bottom: .5rem; }
.problem-num { font-weight: 700; }
.badge { font-size: .8rem; padding: .15rem .6rem; border-radius: 99px; border: 1px solid var(--line); color: var(--muted); white-space: nowrap; }
.badge.ok { background: var(--ok-bg); color: var(--ok); border-color: transparent; }
.badge.bad { background: var(--bad-bg); color: var(--bad); border-color: transparent; }
.prompt { font-size: 1.1rem; margin: .25rem 0 1rem; }

/* answer controls */
.answer-row { display: flex; flex-wrap: wrap; gap: .6rem; align-items: center; }
input[type=text], input[type=password] { font: inherit; padding: .5rem .7rem; border: 1px solid var(--line); border-radius: 8px; background: var(--bg); color: var(--ink); min-width: 14rem; }
.hint { color: var(--muted); font-size: .85rem; margin-top: .4rem; }
.choices { list-style: none; padding: 0; margin: 0 0 1rem; display: grid; gap: .5rem; }
.choices label { display: flex; align-items: center; gap: .6rem; padding: .55rem .8rem; border: 1px solid var(--line); border-radius: 8px; cursor: pointer; background: var(--bg); }
.choices label:has(input:checked) { border-color: var(--accent); box-shadow: 0 0 0 1px var(--accent); }
.btn { padding: .5rem 1rem; border-radius: 8px; border: 1px solid var(--accent); background: var(--accent); color: var(--accent-ink); font-weight: 600; }
.btn.secondary { background: transparent; color: var(--accent); }
.btn:disabled { opacity: .5; cursor: default; }
.feedback { margin-top: .9rem; padding: .6rem .9rem; border-radius: 8px; }
.feedback.ok { background: var(--ok-bg); color: var(--ok); }
.feedback.bad { background: var(--bad-bg); color: var(--bad); }
.feedback.note { background: var(--note-bg); }

/* login */
.auth { max-width: 26rem; margin: 8vh auto; padding: 0 1rem; }
.auth .card { padding: 1.5rem; }
.auth label { display: block; font-weight: 600; margin: .8rem 0 .25rem; }
.auth input { width: 100%; }
.auth .btn { width: 100%; margin-top: 1.2rem; }
.tabs { display: flex; gap: .5rem; margin-bottom: .5rem; }
.tab { flex: 1; padding: .5rem; border: 1px solid var(--line); background: transparent; color: var(--ink); border-radius: 8px; }
.tab[aria-selected=true] { background: var(--accent); color: var(--accent-ink); border-color: var(--accent); }
.error { color: var(--bad); margin-top: .8rem; }

/* course list + gradebook */
.course-list { display: grid; gap: .8rem; }
.course-item { display: block; text-decoration: none; color: inherit; }
.course-item:hover { border-color: var(--accent); }
.table-wrap { overflow-x: auto; }
table { border-collapse: collapse; width: 100%; background: var(--panel); }
th, td { border: 1px solid var(--line); padding: .45rem .7rem; text-align: left; white-space: nowrap; }
th { background: var(--bg); font-size: .85rem; }
td.num { text-align: center; }

/* ---------- editor ---------- */
.row { display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; margin: .5rem 0; }
.row.end { justify-content: flex-end; }
.grow { flex: 1 1 12rem; min-width: 8rem; }
.muted { color: var(--muted); }
.field { margin: 1rem 0; }
.field > label, .card > label, dialog.modal label { display: block; font-weight: 600; margin-bottom: .3rem; }
textarea, select { font: inherit; padding: .5rem .7rem; border: 1px solid var(--line); border-radius: 8px; background: var(--bg); color: var(--ink); max-width: 100%; }
.field textarea, .field input[type=text] { width: 100%; }
.row input[type=text] { min-width: 0; }
input.tiny { width: 3rem; text-align: center; }
input.num { width: 5rem; }
input.wide { width: 9rem; }
.pform h2, dialog.modal h2 { margin: 0 0 .5rem; font-size: 1.15rem; }
fieldset.block, details.block, div.block { border: 1px solid var(--line); border-radius: var(--radius); padding: .6rem .9rem; margin: 1rem 0; }
fieldset.block legend { font-weight: 600; padding: 0 .3rem; }
details.block > summary { cursor: pointer; font-weight: 600; }
.linkbtn { background: none; border: 0; color: var(--accent); padding: .2rem 0; text-decoration: underline; }
.linkbtn:disabled { color: var(--muted); text-decoration: none; cursor: default; }
.linkbtn.indent { margin-left: 1rem; }
.icon { border: 1px solid var(--line); background: var(--panel); color: var(--ink); border-radius: 6px; width: 1.9rem; height: 1.9rem; line-height: 1; padding: 0; }
.icon:hover:not(:disabled) { border-color: var(--accent); }
.icon:disabled { opacity: .35; cursor: default; }
.btn.full { width: 100%; margin-top: .75rem; }
.btn.danger { background: var(--bad); border-color: var(--bad); color: #fff; }
.btn.danger-outline { background: transparent; color: var(--bad); border-color: var(--bad); }
.danger-zone { border-color: var(--bad); }
.tip { background: var(--note-bg); }
.code { font-size: 1.4rem; letter-spacing: .12em; font-weight: 700; }
.check { display: flex; gap: .4rem; align-items: center; margin-top: .6rem; }
.json { width: 100%; font-family: ui-monospace, Menlo, Consolas, monospace; font-size: .85rem; }
.snippet { margin: .25rem 0 .75rem; font-family: ui-monospace, Menlo, Consolas, monospace; font-size: .9rem; color: var(--muted); overflow-wrap: anywhere; }

/* outline (left column of the editor) */
.outline-title { margin-top: 1rem; }
.o-chapter { margin: .8rem 0; }
.o-head { display: flex; align-items: center; gap: .25rem; flex-wrap: wrap; }
.o-title { font-weight: 600; flex: 1 1 100%; }
.o-section { display: flex; align-items: center; gap: .25rem; margin-top: .25rem; }
.o-link { flex: 1; display: flex; justify-content: space-between; gap: .5rem; padding: .35rem .5rem; border-radius: 6px; text-decoration: none; color: var(--ink); font-size: .95rem; min-width: 0; }
.o-link:hover { background: var(--bg); }
.o-section.current .o-link { background: var(--accent); color: var(--accent-ink); }
.o-link .count { opacity: .75; font-size: .8rem; }

/* live preview while writing a problem */
.preview { border: 1px dashed var(--line); border-radius: var(--radius); padding: .6rem .9rem; margin: 1rem 0; }
.okline { color: var(--ok); }
.errors { color: var(--bad); margin: .3rem 0; padding-left: 1.2rem; }
.sample { border-top: 1px solid var(--line); padding-top: .5rem; margin-top: .6rem; }
.sample .prompt { margin: .2rem 0 .5rem; }
.preview-choices { list-style: none; padding: 0; margin: 0 0 .4rem; display: grid; gap: .25rem; }
.preview-choices li { display: flex; gap: .5rem; }
.preview-choices .mark { width: 1.2rem; color: var(--ok); }
.preview-choices li.right { font-weight: 600; }

/* dialogs and messages */
dialog.modal { border: 1px solid var(--line); border-radius: var(--radius); background: var(--panel); color: var(--ink); padding: 1.25rem; width: min(28rem, calc(100vw - 2rem)); }
dialog.modal::backdrop { background: rgba(0, 0, 0, .45); }
dialog.modal input[type=text] { width: 100%; }
.flash { position: fixed; left: 50%; bottom: 1.25rem; transform: translateX(-50%); padding: .6rem 1rem; border-radius: 8px; background: var(--brand); color: #fff; box-shadow: 0 4px 16px rgba(0, 0, 0, .25); max-width: calc(100vw - 2rem); z-index: 10; }
.flash.bad { background: var(--bad); }
.flash[hidden] { display: none; }

/* math drawn by mathfallback.js when KaTeX is not available */
.tex { font-family: "Cambria Math", "STIX Two Math", "Latin Modern Math", Georgia, "Times New Roman", serif; font-size: 1.08em; }
.tex .op { margin: 0 .16em; }
.tex .rel { margin: 0 .28em; }
.tex sup, .tex sub { font-size: .7em; line-height: 0; }
.tex .frac { display: inline-flex; flex-direction: column; vertical-align: middle; text-align: center; margin: 0 .15em; }
.tex .frac .num { border-bottom: 1.5px solid currentColor; padding: 0 .25em .05em; }
.tex .frac .den { padding: .05em .25em 0; }
.tex .sqrt .rad { border-top: 1.5px solid currentColor; padding: 0 .1em; margin-left: .05em; }

/* several answer boxes in one problem */
.multi { margin-top: .4rem; }
.multi-row { display: flex; align-items: center; gap: .6rem; margin: .45rem 0 .1rem; }
.multi-label { min-width: 5.5rem; text-align: right; }
.multi-row input { flex: 1; max-width: 22rem; }
.multi-hint { margin-left: 6.1rem; }
.multi input.ok { border-color: var(--ok); background: var(--ok-bg); }
.multi input.bad { border-color: var(--bad); background: var(--bad-bg); }
.part-block { border: 1px solid var(--line); border-radius: 8px; padding: .6rem .8rem; margin: .6rem 0; background: var(--bg); }
.preview-choices .lbl { display: inline-block; min-width: 4rem; }

/* live equation preview under answer boxes */
.live { margin: .35rem 0 .1rem; min-height: 1.6rem; color: var(--ink); }
.live-label { color: var(--muted); font-size: .85rem; }
.live.soft .live-body { color: var(--muted); font-size: .85rem; }
.multi-live { margin-left: 6.1rem; }