/* Cổng học lập trình — giao diện sáng, thân thiện, các khối màu lớn bo tròn. */
:root {
  --ink: #1B2340; --ink-2: #4A5372; --ink-3: #7C849E;
  --paper: #FFFDF8; --card: #FFFFFF; --line: #E9E4D8; --soft: #F6F2E8;
  --py: #FFD23F; --py-ink: #3A2E00; --py-deep: #306998;
  --cpp: #3D6BFF; --cpp-ink: #FFFFFF; --cpp-soft: #E7EDFF;
  --sql: #FF7A45; --sql-ink: #FFFFFF; --sql-soft: #FFEBE1;
  --ok: #17A673; --ok-soft: #E2F6EE; --bad: #D8383B; --bad-soft: #FDE9E9;
  --r-lg: 28px; --r-md: 18px; --r-sm: 12px;
  --mono: "JetBrains Mono", ui-monospace, Consolas, monospace;
  --shadow: 0 10px 30px rgba(27, 35, 64, .08);
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; font-family: "Be Vietnam Pro", system-ui, -apple-system, "Segoe UI", sans-serif; color: var(--ink); background: var(--paper); line-height: 1.6; -webkit-font-smoothing: antialiased; }
h1, h2, h3 { line-height: 1.2; margin: 0; letter-spacing: -.01em; }
p { margin: 0; }
a { color: inherit; }
button { font: inherit; cursor: pointer; }
code, pre, textarea.code { font-family: var(--mono); }
.skip { position: absolute; left: -9999px; }
.skip:focus { left: 12px; top: 12px; background: var(--ink); color: #fff; padding: 8px 14px; border-radius: 10px; z-index: 99; }
.noscript { padding: 40px; text-align: center; }
.wrap { max-width: 1120px; margin: 0 auto; padding: 0 20px; }
.muted { color: var(--ink-3); }
.small { font-size: 14px; }
.spacer { flex: 1; }
.row { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
:focus-visible { outline: 3px solid var(--cpp); outline-offset: 2px; border-radius: 8px; }

/* Nút */
.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; padding: 11px 20px; border-radius: 999px; border: 2px solid var(--ink); background: var(--card); color: var(--ink); font-weight: 700; font-size: 15px; text-decoration: none; transition: transform .12s, box-shadow .12s, background .12s; white-space: nowrap; }
.btn:hover { transform: translateY(-1px); box-shadow: 0 4px 0 var(--ink); }
.btn:active { transform: translateY(1px); box-shadow: none; }
.btn:disabled { opacity: .55; cursor: not-allowed; transform: none; box-shadow: none; }
.btn-primary { background: var(--ink); color: #fff; }
.btn-primary:hover { box-shadow: 0 4px 0 var(--py); }
.btn-run { background: var(--ok); border-color: var(--ok); color: #fff; }
.btn-run:hover { box-shadow: 0 4px 0 #0E7A54; }
.btn-ghost { border-color: transparent; background: transparent; }
.btn-ghost:hover { background: var(--soft); box-shadow: none; transform: none; }
.btn-sm { padding: 7px 14px; font-size: 14px; }

/* Thanh trên */
.top { position: sticky; top: 0; z-index: 20; background: rgba(255, 253, 248, .92); backdrop-filter: blur(8px); border-bottom: 1px solid var(--line); }
.top-in { display: flex; align-items: center; gap: 14px; height: 66px; }
.brand { display: inline-flex; align-items: center; gap: 10px; font-weight: 800; font-size: 18px; text-decoration: none; }
.brand-mark { width: 36px; height: 36px; border-radius: 11px; background: var(--ink); color: var(--py); display: grid; place-items: center; font-family: var(--mono); font-weight: 700; font-size: 15px; }
.top nav { display: flex; gap: 4px; }
.top nav a { padding: 8px 12px; border-radius: 999px; text-decoration: none; font-weight: 600; font-size: 15px; color: var(--ink-2); }
.top nav a:hover { background: var(--soft); color: var(--ink); }
.who { font-weight: 600; font-size: 15px; }

/* Trang giới thiệu */
.hero { padding: 64px 0 40px; display: grid; grid-template-columns: 1.1fr .9fr; gap: 40px; align-items: center; }
.hero h1 { font-size: clamp(36px, 5.4vw, 62px); font-weight: 800; }
.hero h1 mark { background: var(--py); color: var(--py-ink); padding: 0 .18em; border-radius: 12px; }
.hero .lead { margin-top: 18px; font-size: 19px; color: var(--ink-2); max-width: 34em; }
.hero .cta { margin-top: 28px; }
.hero-art { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.tile { border-radius: var(--r-lg); padding: 22px; min-height: 150px; display: flex; flex-direction: column; justify-content: space-between; font-weight: 800; font-size: 26px; }
.tile small { font-family: var(--mono); font-weight: 500; font-size: 13px; opacity: .85; white-space: pre; display: block; line-height: 1.5; }
.tile.py { background: var(--py); color: var(--py-ink); }
.tile.cpp { background: var(--cpp); color: var(--cpp-ink); }
.tile.sql { background: var(--sql); color: var(--sql-ink); grid-column: span 2; min-height: 120px; }
.sec { padding: 56px 0; }
.sec-head { max-width: 40em; margin-bottom: 28px; }
.sec-head h2 { font-size: clamp(26px, 3.4vw, 36px); font-weight: 800; }
.sec-head p { margin-top: 10px; color: var(--ink-2); font-size: 17px; }
.band { background: var(--soft); border-block: 1px solid var(--line); }
.steps { list-style: none; padding: 0; margin: 0; display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; counter-reset: s; }
.steps li { background: var(--card); border: 1px solid var(--line); border-radius: var(--r-md); padding: 24px; counter-increment: s; }
.steps li::before { content: counter(s); display: grid; place-items: center; width: 40px; height: 40px; border-radius: 50%; background: var(--ink); color: var(--py); font-weight: 800; margin-bottom: 14px; }
.steps h3 { font-size: 18px; margin-bottom: 6px; }
.steps p { color: var(--ink-2); font-size: 15px; }
.faq details { background: var(--card); border: 1px solid var(--line); border-radius: var(--r-sm); padding: 16px 20px; margin-bottom: 10px; }
.faq summary { font-weight: 700; cursor: pointer; }
.faq p { margin-top: 10px; color: var(--ink-2); }
.foot { padding: 28px 0 40px; color: var(--ink-3); font-size: 14px; border-top: 1px solid var(--line); }

/* Thẻ môn học */
.subjects { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }
.subj { position: relative; border-radius: var(--r-lg); padding: 26px; display: flex; flex-direction: column; gap: 12px; min-height: 290px; text-decoration: none; border: 0; text-align: left; transition: transform .15s, box-shadow .15s; width: 100%; }
.subj:hover { transform: translateY(-4px) rotate(-.4deg); box-shadow: var(--shadow); }
.subj.python { background: var(--py); color: var(--py-ink); }
.subj.cpp { background: var(--cpp); color: var(--cpp-ink); }
.subj.sql { background: var(--sql); color: var(--sql-ink); }
.subj .glyph { font-family: var(--mono); font-weight: 700; font-size: 15px; background: rgba(255, 255, 255, .28); border-radius: 12px; padding: 6px 12px; align-self: flex-start; }
.subj.python .glyph { background: rgba(58, 46, 0, .12); }
.subj h3 { font-size: 34px; font-weight: 800; }
.subj .tag { font-weight: 700; font-size: 16px; }
.subj .desc { font-size: 15px; opacity: .92; }
.subj .meta { margin-top: auto; display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 14px; }
.subj .go { margin-left: auto; width: 42px; height: 42px; border-radius: 50%; background: rgba(255, 255, 255, .95); color: var(--ink); display: grid; place-items: center; font-size: 20px; flex-shrink: 0; }
.bar { height: 10px; border-radius: 999px; background: rgba(255, 255, 255, .35); overflow: hidden; flex: 1; }
.bar i { display: block; height: 100%; width: 0; background: #fff; border-radius: 999px; transition: width .5s; }
.bar.dark { background: var(--line); }
.bar.dark i { background: var(--ok); }
.hello { padding: 44px 0 26px; }
.hello h1 { font-size: clamp(28px, 4vw, 42px); font-weight: 800; }
.hello p { margin-top: 8px; color: var(--ink-2); font-size: 17px; }

/* Trang khóa học */
.course-head { border-radius: var(--r-lg); padding: 30px; margin: 28px 0 24px; display: grid; grid-template-columns: 1fr auto; gap: 20px; align-items: end; }
.course-head.cpp { background: var(--cpp); color: #fff; }
.course-head.sql { background: var(--sql); color: #fff; }
.course-head h1 { font-size: clamp(30px, 4.4vw, 46px); font-weight: 800; }
.course-head .stat { font-weight: 800; font-size: 30px; text-align: right; }
.course-head .stat small { display: block; font-size: 13px; font-weight: 600; opacity: .9; }
.crumbs { margin-top: 22px; font-size: 14px; font-weight: 600; color: var(--ink-3); display: flex; gap: 8px; flex-wrap: wrap; }
.crumbs a { text-decoration: none; color: var(--ink-2); }
.crumbs a:hover { text-decoration: underline; }
.chapters { display: grid; gap: 14px; padding-bottom: 60px; }
.chap { background: var(--card); border: 1px solid var(--line); border-radius: var(--r-md); overflow: hidden; }
.chap > summary { list-style: none; display: flex; align-items: center; gap: 14px; padding: 18px 22px; cursor: pointer; font-weight: 700; font-size: 17px; }
.chap > summary::-webkit-details-marker { display: none; }
.chap .num { width: 38px; height: 38px; border-radius: 12px; display: grid; place-items: center; font-weight: 800; background: var(--soft); flex-shrink: 0; }
.chap.done .num { background: var(--ok); color: #fff; }
.chap .count { font-size: 14px; font-weight: 600; color: var(--ink-3); white-space: nowrap; }
.chap-body { padding: 0 22px 20px; border-top: 1px solid var(--line); }
.exlist { list-style: none; margin: 14px 0 0; padding: 0; display: grid; gap: 8px; }
.exlist a { display: flex; align-items: center; gap: 12px; padding: 12px 16px; border-radius: var(--r-sm); background: var(--soft); text-decoration: none; font-weight: 600; }
.exlist a:hover { background: #EFE9DA; }
.exlist .no { font-family: var(--mono); font-size: 13px; color: var(--ink-3); width: 3.2em; }
.pill { font-size: 13px; font-weight: 700; padding: 3px 10px; border-radius: 999px; background: #fff; color: var(--ink-3); white-space: nowrap; }
.pill.ok { background: var(--ok); color: #fff; }
.pill.try { background: var(--bad-soft); color: var(--bad); }

/* Văn bản lý thuyết / đề bài */
.md { font-size: 16px; }
.md p { margin: 12px 0; }
.md ul { margin: 12px 0; padding-left: 22px; }
.md li { margin: 5px 0; }
.md code { background: var(--soft); border: 1px solid var(--line); padding: 1px 6px; border-radius: 6px; font-size: .9em; }
.md pre { background: var(--ink); color: #E8ECF8; padding: 16px 18px; border-radius: var(--r-sm); overflow-x: auto; font-size: 14px; line-height: 1.55; margin: 14px 0; }
.md pre code { background: none; border: 0; padding: 0; color: inherit; font-size: inherit; }

/* Trang bài tập */
.work { display: grid; grid-template-columns: minmax(0, 5fr) minmax(0, 6fr); gap: 22px; padding: 18px 0 60px; align-items: start; }
.work > * { min-width: 0; }
.panel { background: var(--card); border: 1px solid var(--line); border-radius: var(--r-md); padding: 22px; }
.panel h1 { font-size: 24px; font-weight: 800; }
.panel h2 { font-size: 15px; font-weight: 800; margin: 20px 0 8px; text-transform: none; }
.exmeta { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 10px; }
.sample { background: var(--soft); border: 1px solid var(--line); border-radius: var(--r-sm); padding: 12px 14px; font-family: var(--mono); font-size: 13.5px; white-space: pre; overflow-x: auto; margin: 0; line-height: 1.5; }
details.fold { border: 1px solid var(--line); border-radius: var(--r-sm); margin-top: 12px; }
details.fold > summary { padding: 11px 14px; font-weight: 700; cursor: pointer; font-size: 15px; }
details.fold > div { padding: 0 14px 12px; }
table.schema { border-collapse: collapse; width: 100%; font-size: 13.5px; margin: 6px 0 14px; }
table.schema caption { text-align: left; font-family: var(--mono); font-weight: 700; padding: 6px 0; }
table.schema td { border-top: 1px solid var(--line); padding: 5px 8px 5px 0; }
table.schema td:first-child { font-family: var(--mono); }
.editor { border: 2px solid var(--ink); border-radius: var(--r-md); overflow: hidden; background: #fff; }
.editor-head { display: flex; align-items: center; gap: 10px; padding: 10px 12px 10px 16px; background: var(--ink); color: #fff; }
.editor-head .file { font-family: var(--mono); font-size: 13.5px; opacity: .9; }
.editor-head kbd { font-family: var(--mono); font-size: 11.5px; border: 1px solid rgba(255, 255, 255, .35); border-radius: 5px; padding: 1px 5px; }
.editor-head .btn { border-color: #fff; }
.editor-head .btn-ghost { color: #fff; border-color: rgba(255, 255, 255, .35); }
.editor-head .btn-ghost:hover { background: rgba(255, 255, 255, .12); }
.code-area { position: relative; display: flex; height: 380px; }
.gutter { width: 46px; background: var(--soft); color: var(--ink-3); font-family: var(--mono); font-size: 14px; line-height: 22px; text-align: right; padding: 12px 8px 12px 0; overflow: hidden; user-select: none; flex-shrink: 0; white-space: pre; }
.gutter .err { background: var(--bad); color: #fff; display: block; margin-right: -8px; padding-right: 8px; }
textarea.code { flex: 1; border: 0; outline: 0; resize: none; padding: 12px 14px; font-size: 14px; line-height: 22px; color: var(--ink); background: #fff; white-space: pre; overflow: auto; tab-size: 4; }
.stdin { border-top: 1px solid var(--line); padding: 10px 14px; background: var(--soft); }
.stdin label { font-size: 13px; font-weight: 700; display: block; margin-bottom: 4px; }
.stdin textarea { width: 100%; border: 1px solid var(--line); border-radius: 8px; padding: 8px 10px; font-family: var(--mono); font-size: 13.5px; resize: vertical; min-height: 44px; background: #fff; }
.result { margin-top: 16px; border-radius: var(--r-md); border: 1px solid var(--line); background: var(--card); overflow: hidden; }
.result-head { padding: 12px 16px; font-weight: 800; display: flex; align-items: center; gap: 10px; background: var(--soft); }
.result.ok .result-head { background: var(--ok-soft); color: #0C6B49; }
.result.bad .result-head { background: var(--bad-soft); color: #A1272A; }
.result-body { padding: 14px 16px; }
.result pre { margin: 0; font-size: 13.5px; line-height: 1.5; white-space: pre; overflow-x: auto; max-height: 340px; }
.result .fix { margin-top: 8px; color: var(--ink-2); font-size: 15px; }
.result h3 { font-size: 14px; margin: 14px 0 6px; }
.score { font-size: 15px; }
.stamp { display: inline-grid; place-items: center; width: 54px; height: 54px; border-radius: 50%; background: var(--ok); color: #fff; font-weight: 800; font-size: 20px; flex-shrink: 0; }
.tests { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 10px; }
.tests span { font-size: 13px; font-weight: 700; padding: 4px 10px; border-radius: 999px; background: var(--ok-soft); color: #0C6B49; }
.tests span.bad { background: var(--bad-soft); color: #A1272A; }
.navrow { display: flex; gap: 10px; margin-top: 16px; }
.spin { width: 15px; height: 15px; border: 2.5px solid rgba(255, 255, 255, .45); border-top-color: #fff; border-radius: 50%; display: inline-block; animation: sp .7s linear infinite; }
@keyframes sp { to { transform: rotate(360deg); } }

/* Hộp thoại, thông báo */
.overlay { position: fixed; inset: 0; background: rgba(27, 35, 64, .5); display: grid; place-items: center; padding: 20px; z-index: 50; }
.dialog { background: var(--card); border-radius: var(--r-lg); padding: 30px; width: min(430px, 100%); box-shadow: var(--shadow); }
.dialog h2 { font-size: 26px; font-weight: 800; }
.dialog .tabs { display: flex; gap: 6px; background: var(--soft); padding: 5px; border-radius: 999px; margin: 18px 0; }
.dialog .tabs button { flex: 1; border: 0; background: transparent; padding: 9px; border-radius: 999px; font-weight: 700; color: var(--ink-2); }
.dialog .tabs button.on { background: var(--ink); color: #fff; }
.field { display: block; margin-bottom: 14px; }
.field span { display: block; font-weight: 700; font-size: 14px; margin-bottom: 5px; }
.field input { width: 100%; padding: 12px 14px; border: 2px solid var(--line); border-radius: var(--r-sm); font: inherit; }
.field input:focus { border-color: var(--ink); outline: 0; }
.form-err { background: var(--bad-soft); color: #A1272A; border-radius: var(--r-sm); padding: 10px 14px; font-size: 14.5px; font-weight: 600; margin-bottom: 14px; }
.dialog .btn { width: 100%; }
#toasts { position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%); display: grid; gap: 8px; z-index: 60; }
.toast { background: var(--ink); color: #fff; padding: 12px 20px; border-radius: 999px; font-weight: 600; font-size: 15px; box-shadow: var(--shadow); }
table.admin { width: 100%; border-collapse: collapse; font-size: 14.5px; }
table.admin th, table.admin td { text-align: left; padding: 10px 12px; border-bottom: 1px solid var(--line); }
table.admin th { font-size: 13px; color: var(--ink-3); }
.kpis { display: grid; grid-template-columns: repeat(4, 1fr); gap: 14px; margin: 20px 0; }
.kpi { background: var(--card); border: 1px solid var(--line); border-radius: var(--r-md); padding: 18px; }
.kpi b { display: block; font-size: 28px; font-weight: 800; }
.kpi.warn { background: var(--bad-soft); border-color: #F3C2C3; }
.scroll-x { overflow-x: auto; }

@media (max-width: 900px) {
  .hero { grid-template-columns: 1fr; padding-top: 40px; }
  .subjects, .steps { grid-template-columns: 1fr; }
  .subj { min-height: 0; }
  .work { grid-template-columns: minmax(0, 1fr); }
  .top nav { display: none; }
  .course-head { grid-template-columns: 1fr; }
  .course-head .stat { text-align: left; }
  .kpis { grid-template-columns: 1fr 1fr; }
  .code-area { height: 320px; }
}
@media (max-width: 520px) {
  .wrap { padding: 0 16px; }
  .who { display: none; }
  .editor-head kbd { display: none; }
  .panel { padding: 18px; }
}
@media (prefers-reduced-motion: reduce) { * { transition: none !important; animation: none !important; } html { scroll-behavior: auto; } }