:root {
  --bg: #f4f5f7;
  --panel: #ffffff;
  --text: #20242a;
  --muted: #5f6772;
  --rule: #dfe2e6;
  --link: #0b5aa6;
  --ink: #1f2429;           /* header and title band */
  --ink-2: #2b3138;
  --on-ink: #eef0f2;
  --red: #c8102e;           /* NIU red */
  --code-bg: #eef0f3;
  --mark: #fff0a0;
  --sans: "IBM Plex Sans", "Helvetica Neue", Arial, sans-serif;
  --mono: "IBM Plex Mono", Menlo, Consolas, monospace;
  --radius: 6px;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #15181c;
    --panel: #1c2026;
    --text: #e3e6ea;
    --muted: #99a1ab;
    --rule: #2f353d;
    --link: #82b6ee;
    --ink: #0e1013;
    --ink-2: #181b20;
    --code-bg: #252a31;
    --mark: #5a4b12;
    --red: #e0354f;
  }
  .prose img { background: #fff; border-radius: 2px; }
}

* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--text); font: 17px/1.65 var(--sans); min-height: 100vh; display: flex; flex-direction: column; }
main { flex: 1 0 auto; width: 100%; }
a { color: var(--link); text-decoration: none; }
a:hover { text-decoration: underline; }
code, pre { font-family: var(--mono); font-size: .88em; }
mark { background: var(--mark); color: inherit; }
.wrap { max-width: 980px; margin: 0 auto; padding: 0 20px; }
h1, h2, h3 { font-weight: 600; line-height: 1.25; }

/* header */
.bar { background: var(--ink); }
.bar .wrap { display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 6px 24px; padding-top: 12px; padding-bottom: 12px; }
.bar .course { color: #fff; display: flex; align-items: baseline; gap: 10px; }
.bar .course:hover { text-decoration: none; }
.bar .course b { letter-spacing: .03em; }
.bar .course b::before { content: ""; display: inline-block; width: 10px; height: 10px; background: var(--red); margin-right: 8px; }
.bar .course span { color: var(--on-ink); opacity: .6; font-size: .9rem; }
.bar nav { display: flex; flex-wrap: wrap; gap: 4px 22px; font-size: .95rem; }
.bar nav a { color: var(--on-ink); opacity: .72; padding: 2px 0; }
.bar nav a:hover { opacity: 1; text-decoration: none; }
.bar nav a.on { opacity: 1; box-shadow: inset 0 -2px 0 var(--red); }
@media (max-width: 720px) { .bar .course span { display: none; } }

/* title band */
.hero { background: linear-gradient(180deg, var(--ink-2), var(--ink)); color: var(--on-ink); border-bottom: 4px solid var(--red); }
.hero .wrap { padding-top: 44px; padding-bottom: 40px; }
.hero h1 { color: #fff; font-size: clamp(1.8rem, 4.5vw, 2.6rem); margin: 0 0 12px; max-width: 760px; }
.hero p { margin: 0 0 10px; max-width: 720px; opacity: .88; }
.hero .kicker { color: #ff8a98; font-size: .85rem; letter-spacing: .06em; text-transform: uppercase; opacity: 1; margin-bottom: 12px; }
.hero .who { font-size: .95rem; opacity: .7; }
.hero .actions { margin-top: 22px; display: flex; gap: 10px; flex-wrap: wrap; }
.btn { display: inline-block; padding: 9px 18px; border-radius: var(--radius); border: 1px solid rgba(255,255,255,.35); color: #fff; font-weight: 500; }
.btn:hover { text-decoration: none; border-color: #fff; }
.btn.solid { background: var(--red); border-color: var(--red); }

/* main */
main.wrap { padding-top: 36px; padding-bottom: 56px; }
main h2 { font-size: 1.3rem; margin: 40px 0 14px; }
p { margin: 0 0 14px; }
.small { color: var(--muted); font-size: .92rem; margin-top: 36px; }
ul, ol { padding-left: 1.3em; }

/* home */
.tiles { display: grid; grid-template-columns: repeat(4, 1fr); gap: 14px; }
.tile { background: var(--panel); border: 1px solid var(--rule); border-top: 3px solid var(--red); border-radius: var(--radius); padding: 16px 18px; color: var(--text); display: flex; flex-direction: column; gap: 4px; }
.tile:hover { text-decoration: none; border-color: var(--muted); border-top-color: var(--red); }
.tile b { color: var(--link); font-size: 1.05rem; }
.tile span { color: var(--muted); font-size: .9rem; line-height: 1.45; }
@media (max-width: 820px) { .tiles { grid-template-columns: repeat(2, 1fr); } }
@media (max-width: 460px) { .tiles { grid-template-columns: 1fr; } }

ol.topics { list-style: none; padding: 0; margin: 0; display: grid; grid-template-columns: repeat(2, 1fr); gap: 0 28px; }
ol.topics a { display: flex; gap: 14px; align-items: baseline; padding: 11px 0; border-bottom: 1px solid var(--rule); color: var(--text); }
ol.topics a:hover { text-decoration: none; }
ol.topics a:hover b { color: var(--link); }
ol.topics .n, .module .n, .case .n { color: var(--red); font-weight: 600; font-variant-numeric: tabular-nums; }
ol.topics b { font-weight: 500; }
ol.topics small { display: block; color: var(--muted); font-size: .85rem; }
@media (max-width: 680px) { ol.topics { grid-template-columns: 1fr; } }

.split { display: grid; grid-template-columns: 1fr 1fr; gap: 0 36px; }
@media (max-width: 680px) { .split { grid-template-columns: 1fr; } }

/* materials */
.module { background: var(--panel); border: 1px solid var(--rule); border-radius: var(--radius); padding: 22px 24px; margin-bottom: 18px; scroll-margin-top: 16px; }
.module > header { display: flex; gap: 16px; align-items: flex-start; }
.module > header .n { font-size: 1.4rem; line-height: 1.2; min-width: 1.6em; }
.module h2 { margin: 0 0 4px; font-size: 1.2rem; }
.module > header p { color: var(--muted); font-size: .95rem; margin: 0; }
.when { white-space: nowrap; font-size: .85rem; color: var(--muted); border: 1px solid var(--rule); border-radius: 99px; padding: 0 8px; margin-left: 4px; }
.module .cols { display: grid; grid-template-columns: 1fr 1fr; gap: 0 32px; margin: 14px 0 0 calc(2.24rem + 16px); }
.module h3 { font-size: .8rem; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); margin: 6px 0 6px; }
.module h3 em { font-style: normal; text-transform: none; letter-spacing: 0; opacity: .8; }
.module ul { list-style: none; margin: 0; padding: 0; }
.module li { padding: 5px 0; border-top: 1px solid var(--rule); }
.module li:first-child { border-top: 0; }
.alt { color: var(--muted); font-size: .85rem; margin-left: 4px; }
.alt::before { content: "· "; }
.none { color: var(--muted); }
@media (max-width: 720px) {
  .module { padding: 18px; }
  .module .cols { grid-template-columns: 1fr; margin-left: 0; }
  .module .cols > div + div { margin-top: 10px; }
}

/* homework table */
table { border-collapse: collapse; width: 100%; }
table.grid { background: var(--panel); border: 1px solid var(--rule); border-radius: var(--radius); overflow: hidden; }
table.grid th { text-align: left; font-size: .8rem; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); font-weight: 600; padding: 12px 16px; border-bottom: 1px solid var(--rule); }
table.grid td { padding: 13px 16px; border-bottom: 1px solid var(--rule); vertical-align: top; }
table.grid tr:last-child td { border-bottom: 0; }
table.grid td:first-child { white-space: nowrap; font-weight: 500; }
table.grid .r { text-align: right; }

/* project */
.cases { display: grid; grid-template-columns: repeat(3, 1fr); gap: 14px; }
.case { background: var(--panel); border: 1px solid var(--rule); border-radius: var(--radius); padding: 16px 18px; color: var(--text); display: flex; flex-direction: column; gap: 4px; }
.case:hover { text-decoration: none; border-color: var(--muted); }
.case b { color: var(--link); }
.case > span:last-child { color: var(--muted); font-size: .92rem; line-height: 1.45; }
@media (max-width: 820px) { .cases { grid-template-columns: repeat(2, 1fr); } }
@media (max-width: 520px) { .cases { grid-template-columns: 1fr; } }

/* document pages */
.docbar { display: flex; justify-content: space-between; flex-wrap: wrap; gap: 6px 16px; font-size: .9rem; color: var(--muted); margin-bottom: 16px; }
.prose { background: var(--panel); border: 1px solid var(--rule); border-radius: var(--radius); padding: 8px 40px 36px; overflow-wrap: break-word; }
@media (max-width: 680px) { .prose { padding: 4px 18px 24px; } }
.prose h1 { font-size: 1.9rem; margin: 28px 0 12px; }
.prose h2 { font-size: 1.35rem; margin: 36px 0 10px; }
.prose h3 { font-size: 1.1rem; margin: 26px 0 8px; }
.prose img { max-width: 100%; height: auto; vertical-align: middle; }
.prose p img { max-height: 3.2em; }
.prose blockquote { margin: 16px 0; padding: 4px 16px; border-left: 3px solid var(--red); background: var(--bg); }
.prose pre { background: var(--code-bg); padding: 12px 14px; border-radius: 4px; overflow-x: auto; }
.prose :not(pre) > code { background: var(--code-bg); padding: 1px 4px; border-radius: 3px; }
.prose table { display: block; overflow-x: auto; width: auto; max-width: 100%; margin: 14px 0; font-size: .93rem; }
.prose th, .prose td { border: 1px solid var(--rule); padding: 5px 10px; }
.prose th { background: var(--bg); }
.prose hr { border: 0; border-top: 1px solid var(--rule); margin: 28px 0; }
mjx-container[display="true"] { overflow-x: auto; overflow-y: hidden; }

.foot { background: var(--ink); color: var(--on-ink); font-size: .85rem; }
.foot .wrap { display: flex; justify-content: space-between; flex-wrap: wrap; gap: 6px 20px; padding-top: 18px; padding-bottom: 22px; opacity: .8; }
.foot a { color: var(--on-ink); text-decoration: underline; text-decoration-color: rgba(255,255,255,.35); }