/* =========================================================
   HọcFree.vn – stylesheet
   ========================================================= */
:root {
  --bg: #f2f3f5;
  --surface: #ffffff;
  --surface-2: #f7f8fa;
  --text: #16181d;
  --text-2: #3a3f4a;
  --muted: #6b7280;
  --line: #e2e5ea;
  --accent: #f04e23;
  --accent-ink: #c73a14;
  --header: #15171c;
  --header-2: #1d2027;
  --header-text: #e9ebef;
  --code-bg: #1b1e25;
  --code-text: #e6e9ef;
  --shadow: 0 1px 2px rgba(16, 24, 40, .06), 0 4px 16px rgba(16, 24, 40, .06);
  --radius: 10px;
  --c-lt: #f04e23;   /* kiến thức lập trình */
  --c-nn: #4f46e5;   /* ngoại ngữ */
  --c-bl: #0d9488;   /* blog */
  --font: "Be Vietnam Pro", system-ui, -apple-system, "Segoe UI", Roboto, Arial, sans-serif;
  --mono: "JetBrains Mono", Consolas, "Courier New", monospace;
  color-scheme: light;
}
html.dark {
  --bg: #0e1014;
  --surface: #161920;
  --surface-2: #1b1f27;
  --text: #e9ebef;
  --text-2: #c8ccd4;
  --muted: #9aa1ad;
  --line: #272b35;
  --accent: #ff6a3d;
  --accent-ink: #ff8a64;
  --header: #0a0b0e;
  --header-2: #12141a;
  --code-bg: #0b0d11;
  --shadow: 0 1px 2px rgba(0, 0, 0, .4), 0 4px 16px rgba(0, 0, 0, .25);
  --c-nn: #818cf8;
  --c-bl: #2dd4bf;
  color-scheme: dark;
}

*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 80px; }
body {
  margin: 0;
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.6;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
}
img { max-width: 100%; height: auto; display: block; }
a { color: inherit; text-decoration: none; }
a:hover { color: var(--accent); }
h1, h2, h3 { line-height: 1.25; margin: 0; letter-spacing: -.01em; }
svg { width: 20px; height: 20px; fill: none; stroke: currentColor; stroke-width: 2; stroke-linecap: round; stroke-linejoin: round; flex: none; }
button { font: inherit; color: inherit; cursor: pointer; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

.container { width: 100%; max-width: 1240px; margin-inline: auto; padding-inline: 20px; }
.skip-link { position: absolute; left: -999px; top: 8px; z-index: 100; background: var(--accent); color: #fff; padding: 8px 14px; border-radius: 6px; }
.skip-link:focus { left: 8px; }

/* ---------- Thanh tiến độ đọc ---------- */
.progress { position: fixed; top: 0; left: 0; height: 3px; width: 0; background: var(--accent); z-index: 60; transition: width .1s linear; }

/* ---------- Header ---------- */
.site-header { position: sticky; top: 0; z-index: 50; }
.topbar { background: var(--header); color: var(--header-text); border-bottom: 1px solid rgba(255, 255, 255, .06); }
.topbar-inner { display: flex; align-items: center; gap: 28px; height: 64px; }
.logo { display: inline-flex; align-items: center; gap: 10px; font-weight: 800; font-size: 1.45rem; letter-spacing: -.02em; color: #fff; }
.logo:hover { color: #fff; }
.logo b { color: var(--accent); font-weight: 800; }
.logo-mark { width: 34px; height: 34px; stroke: none; }
.main-nav ul { display: flex; gap: 4px; list-style: none; margin: 0; padding: 0; }
.main-nav a {
  display: block; padding: 8px 14px; border-radius: 6px;
  font-weight: 600; font-size: .95rem; color: #c9cdd6; position: relative;
}
.main-nav a:hover { color: #fff; background: rgba(255, 255, 255, .06); }
.main-nav a.active { color: #fff; }
.main-nav a.active::after { content: ""; position: absolute; left: 14px; right: 14px; bottom: -14px; height: 3px; background: var(--accent); border-radius: 3px 3px 0 0; }
.topbar-actions { margin-left: auto; display: flex; gap: 6px; }
.icon-btn {
  display: inline-grid; place-items: center; width: 40px; height: 40px;
  border: 0; border-radius: 8px; background: transparent; color: inherit;
}
.icon-btn:hover { background: rgba(255, 255, 255, .08); }
.burger { display: none; }

.trending { background: var(--header-2); color: #aeb3bd; font-size: .85rem; }
.trending-inner { display: flex; align-items: center; gap: 14px; height: 40px; overflow: hidden; }
.trending-label {
  flex: none; font-weight: 700; color: #fff; text-transform: uppercase; font-size: .72rem; letter-spacing: .08em;
  padding: 3px 9px; border-radius: 4px; background: var(--accent);
}
.trending-links { display: flex; gap: 18px; overflow-x: auto; scrollbar-width: none; white-space: nowrap; }
.trending-links::-webkit-scrollbar { display: none; }
.trending-links a:hover { color: #fff; }

/* ---------- Tìm kiếm ---------- */
.search-panel { position: sticky; top: 104px; z-index: 45; background: var(--surface); border-bottom: 1px solid var(--line); box-shadow: var(--shadow); padding-block: 16px; }
.search-form {
  display: flex; align-items: center; gap: 10px; background: var(--surface-2);
  border: 1px solid var(--line); border-radius: 10px; padding: 4px 6px 4px 14px;
}
.search-form:focus-within { border-color: var(--accent); }
.search-form svg { color: var(--muted); }
.search-form input { flex: 1; min-width: 0; border: 0; background: transparent; font: inherit; font-size: 1.05rem; padding: 10px 0; color: var(--text); outline: none; }
.search-form.big { max-width: 640px; margin-top: 18px; background: var(--surface); }
.search-suggest { margin-top: 8px; }
.search-suggest a { display: flex; gap: 12px; align-items: center; padding: 8px; border-radius: 8px; }
.search-suggest a:hover, .search-suggest a.focus { background: var(--surface-2); color: var(--text); }
.search-suggest img { width: 72px; aspect-ratio: 16/9; object-fit: cover; border-radius: 6px; }
.search-suggest small { display: block; color: var(--muted); font-size: .78rem; }
.search-suggest .empty { color: var(--muted); padding: 8px; }
.search-summary { color: var(--muted); margin: 0 0 8px; }
mark { background: rgba(240, 78, 35, .18); color: inherit; border-radius: 3px; padding: 0 2px; }

/* ---------- Nút, thẻ ---------- */
.btn {
  display: inline-flex; align-items: center; gap: 8px; border: 0; border-radius: 8px;
  background: var(--accent); color: #fff; font-weight: 600; padding: 10px 18px; font-size: .95rem;
}
.btn:hover { color: #fff; background: var(--accent-ink); }
.btn.ghost { background: transparent; color: var(--text); border: 1px solid var(--line); }
.btn.ghost:hover { border-color: var(--accent); color: var(--accent); }

.pill {
  display: inline-block; font-size: .72rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase;
  color: #fff; background: var(--accent); padding: 4px 10px; border-radius: 4px;
}
.pill:hover { color: #fff; filter: brightness(1.1); }
.kicker { display: inline-block; font-size: .74rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--accent); }
.cat-kien-thuc-lap-trinh.pill { background: var(--c-lt); }
.cat-ngoai-ngu.pill { background: var(--c-nn); }
.cat-blog.pill { background: var(--c-bl); }
.cat-kien-thuc-lap-trinh.kicker { color: var(--c-lt); }
.cat-ngoai-ngu.kicker { color: var(--c-nn); }
.cat-blog.kicker { color: var(--c-bl); }

.tags { display: flex; flex-wrap: wrap; gap: 8px; }
.tag { font-size: .82rem; padding: 5px 11px; border-radius: 999px; background: var(--surface-2); border: 1px solid var(--line); color: var(--text-2); }
.tag:hover { border-color: var(--accent); color: var(--accent); }

.meta { display: flex; flex-wrap: wrap; align-items: center; gap: 6px 14px; font-size: .82rem; color: var(--muted); }
.meta span { display: inline-flex; align-items: center; gap: 5px; }
.meta svg { width: 14px; height: 14px; }
.meta .by { font-weight: 600; color: var(--text-2); }

/* ---------- Tiêu đề khu vực ---------- */
.section-title { display: flex; align-items: baseline; justify-content: space-between; gap: 12px; border-bottom: 2px solid var(--text); margin-bottom: 8px; }
.section-title h2 { font-size: 1.1rem; font-weight: 800; text-transform: uppercase; letter-spacing: .04em; padding: 0 0 8px; position: relative; }
.section-title h2::after { content: ""; position: absolute; left: 0; bottom: -2px; width: 100%; height: 2px; background: var(--accent); }
.section-title .more { font-size: .85rem; font-weight: 600; color: var(--muted); white-space: nowrap; }
.section-title .more:hover { color: var(--accent); }

/* ---------- Hero ---------- */
.hero { display: grid; grid-template-columns: 2fr 1fr; gap: 16px; margin-top: 24px; }
.hero-side { display: grid; grid-template-rows: 1fr 1fr; gap: 16px; }
.card-overlay { position: relative; border-radius: var(--radius); overflow: hidden; min-height: 222px; background: #222; isolation: isolate; }
.card-overlay.big { min-height: 460px; }
.card-overlay img { position: absolute; inset: 0; width: 100%; height: 100%; object-fit: cover; z-index: -2; transition: transform .5s ease; }
.card-overlay::before { content: ""; position: absolute; inset: 0; z-index: -1; background: linear-gradient(180deg, rgba(0, 0, 0, 0) 25%, rgba(0, 0, 0, .55) 60%, rgba(0, 0, 0, .9) 100%); }
.card-overlay:hover img { transform: scale(1.04); }
.card-overlay-body { position: absolute; left: 0; right: 0; bottom: 0; padding: 20px; color: #fff; }
.card-overlay.big .card-overlay-body { padding: 32px; }
.card-overlay h2, .card-overlay h3 { margin: 10px 0 8px; font-weight: 700; }
.card-overlay h2 { font-size: clamp(1.4rem, 2.6vw, 2.1rem); }
.card-overlay h3 { font-size: 1.1rem; }
.card-overlay h2 a::after, .card-overlay h3 a::after { content: ""; position: absolute; inset: 0; }
.card-overlay a:hover { color: #fff; }
.card-overlay p { margin: 0 0 12px; color: rgba(255, 255, 255, .85); max-width: 640px; }
.card-overlay .meta { color: rgba(255, 255, 255, .75); }
.card-overlay .pill { position: relative; z-index: 1; }

/* ---------- Bố cục 2 cột ---------- */
.layout { display: grid; grid-template-columns: minmax(0, 1fr) 320px; gap: 40px; margin-block: 36px 48px; }

/* ---------- Danh sách bài (kiểu TechSpot) ---------- */
.post-row { display: grid; grid-template-columns: 280px minmax(0, 1fr); gap: 22px; padding-block: 22px; border-bottom: 1px solid var(--line); }
.post-row:last-child { border-bottom: 0; }
.thumb { display: block; border-radius: 8px; overflow: hidden; aspect-ratio: 16 / 9; background: var(--surface-2); }
.thumb img { width: 100%; height: 100%; object-fit: cover; transition: transform .4s ease; }
.thumb:hover img { transform: scale(1.05); }
.post-row h3 { font-size: 1.28rem; font-weight: 700; margin: 4px 0 8px; }
.post-row p { margin: 0 0 10px; color: var(--text-2); font-size: .95rem; display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }

/* ---------- Card ---------- */
.card h3 { font-size: 1.08rem; font-weight: 700; margin: 8px 0; }
.card .thumb { margin-bottom: 12px; }
.card-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; margin-top: 18px; }

/* ---------- Sidebar ---------- */
.sidebar { display: flex; flex-direction: column; gap: 28px; }
.widget { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 20px; }
.widget-title { font-size: .85rem; font-weight: 800; text-transform: uppercase; letter-spacing: .06em; margin-bottom: 14px; padding-bottom: 10px; border-bottom: 1px solid var(--line); }
.popular { list-style: none; margin: 0; padding: 0; }
.popular li + li { border-top: 1px solid var(--line); }
.popular a { display: flex; gap: 14px; padding: 12px 0; align-items: flex-start; }
.popular .num { font-size: 1.6rem; font-weight: 800; line-height: 1; color: var(--accent); min-width: 22px; opacity: .9; }
.popular .t { font-weight: 600; font-size: .94rem; line-height: 1.4; }
.cat-list { list-style: none; margin: 0; padding: 0; }
.cat-list a { display: flex; justify-content: space-between; padding: 9px 0; font-weight: 500; }
.cat-list li + li { border-top: 1px dashed var(--line); }
.cat-list .count { font-size: .8rem; background: var(--surface-2); border: 1px solid var(--line); border-radius: 999px; padding: 1px 10px; color: var(--muted); }
.widget-about p { margin: 0 0 14px; color: var(--text-2); font-size: .94rem; }

/* ---------- Khối chuyên mục trang chủ ---------- */
.band { background: var(--surface); border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); padding-block: 40px; }
.cat-blocks { display: grid; grid-template-columns: repeat(3, 1fr); gap: 32px; }
.cat-block .card { margin-top: 16px; }
.cat-block-list { list-style: none; margin: 8px 0 0; padding: 0; }
.cat-block-list li { padding: 12px 0; border-top: 1px solid var(--line); }
.cat-block-list a { font-weight: 600; display: block; line-height: 1.4; }
.cat-block-list time { font-size: .78rem; color: var(--muted); }
.cat-ngoai-ngu .section-title h2::after { background: var(--c-nn); }
.cat-blog .section-title h2::after { background: var(--c-bl); }

/* ---------- Đầu trang chuyên mục ---------- */
.page-head { background: var(--header-2); color: #fff; padding-block: 36px 40px; position: relative; overflow: hidden; }
.page-head::after { content: ""; position: absolute; right: -80px; top: -120px; width: 420px; height: 420px; border-radius: 50%; background: var(--accent); opacity: .18; filter: blur(30px); }
.page-head.cat-ngoai-ngu::after { background: var(--c-nn); opacity: .3; }
.page-head.cat-blog::after { background: var(--c-bl); opacity: .3; }
.page-head h1 { font-size: clamp(1.8rem, 4vw, 2.6rem); font-weight: 800; margin: 10px 0 8px; }
.page-head p { margin: 0; color: #c3c8d1; max-width: 680px; }
.page-head .breadcrumb { color: #9aa1ad; }
.page-head .breadcrumb a:hover { color: #fff; }
.page-count { display: inline-block; margin-top: 14px; font-size: .8rem; font-weight: 600; padding: 4px 12px; border-radius: 999px; background: rgba(255, 255, 255, .1); }
.hero-cat { margin-top: 28px; }

.breadcrumb { display: flex; flex-wrap: wrap; gap: 8px; font-size: .85rem; color: var(--muted); }

/* ---------- Bài viết ---------- */
.article { min-width: 0; }
.article-head { margin-top: 14px; }
.article-head h1 { font-size: clamp(1.75rem, 3.6vw, 2.6rem); font-weight: 800; margin: 14px 0 12px; }
.lead { font-size: 1.15rem; color: var(--text-2); margin: 0 0 20px; }
.article-meta { display: flex; align-items: center; gap: 12px; padding-block: 14px; border-block: 1px solid var(--line); }
.avatar { display: inline-grid; place-items: center; width: 38px; height: 38px; border-radius: 50%; background: var(--accent); color: #fff; font-weight: 800; font-size: .8rem; flex: none; }
.avatar.lg { width: 56px; height: 56px; font-size: 1rem; }
.article-cover { margin: 24px 0; }
.article-cover img { width: 100%; border-radius: var(--radius); }

.toc { background: var(--surface); border: 1px solid var(--line); border-left: 4px solid var(--accent); border-radius: 8px; padding: 14px 20px; margin-bottom: 28px; }
.toc summary { font-weight: 700; cursor: pointer; }
.toc ol { margin: 10px 0 0; padding-left: 22px; }
.toc li { padding: 3px 0; }
.toc a { color: var(--text-2); }
.toc a:hover { color: var(--accent); }

.prose { font-size: 1.07rem; line-height: 1.8; color: var(--text-2); }
.prose > * + * { margin-top: 1.1em; }
.prose p { margin: 0; }
.prose h2 { font-size: 1.6rem; font-weight: 800; color: var(--text); margin-top: 2em; }
.prose h3 { font-size: 1.25rem; font-weight: 700; color: var(--text); margin-top: 1.6em; }
.prose strong { color: var(--text); }
.prose a { color: var(--accent); text-decoration: underline; text-underline-offset: 3px; text-decoration-thickness: 1px; }
.prose ul, .prose ol { padding-left: 1.4em; margin-bottom: 0; }
.prose li + li { margin-top: .4em; }
.prose li::marker { color: var(--accent); }
.prose code { font-family: var(--mono); font-size: .88em; background: var(--surface-2); border: 1px solid var(--line); padding: .1em .4em; border-radius: 5px; color: var(--text); }
.prose pre {
  position: relative; background: var(--code-bg); color: var(--code-text); border-radius: 10px;
  padding: 18px 20px; overflow-x: auto; font-size: .9rem; line-height: 1.65;
}
.prose pre code { background: none; border: 0; padding: 0; color: inherit; font-size: inherit; }
.copy-btn {
  position: absolute; top: 8px; right: 8px; font-size: .75rem; font-family: var(--font); font-weight: 600;
  border: 1px solid rgba(255, 255, 255, .15); background: rgba(255, 255, 255, .06); color: #cfd3da;
  padding: 4px 10px; border-radius: 6px; opacity: 0; transition: opacity .2s;
}
.prose pre:hover .copy-btn, .copy-btn:focus { opacity: 1; }
.prose blockquote { margin-inline: 0; padding: 16px 20px; border-left: 4px solid var(--accent); background: var(--surface); border-radius: 0 8px 8px 0; color: var(--text); }
.prose .table-wrap { overflow-x: auto; border: 1px solid var(--line); border-radius: 8px; }
.prose table { width: 100%; border-collapse: collapse; font-size: .95rem; background: var(--surface); }
.prose th, .prose td { padding: 10px 14px; text-align: left; border-bottom: 1px solid var(--line); vertical-align: top; }
.prose th { background: var(--surface-2); color: var(--text); font-weight: 700; }
.prose tr:last-child td { border-bottom: 0; }

.article-foot { display: flex; flex-wrap: wrap; justify-content: space-between; align-items: center; gap: 16px; margin-top: 36px; padding-top: 20px; border-top: 1px solid var(--line); }
.share { display: flex; align-items: center; gap: 8px; font-size: .88rem; color: var(--muted); }
.share-btn { display: inline-grid; place-items: center; width: 38px; height: 38px; border-radius: 50%; border: 1px solid var(--line); background: var(--surface); color: var(--text-2); }
.share-btn:hover { color: #fff; border-color: transparent; }
.share-btn.fb:hover { background: #1877f2; }
.share-btn.x:hover { background: #000; }
.share-btn.copy-link:hover, .share-btn.copied { background: var(--accent); color: #fff; }
.share-btn svg { width: 17px; height: 17px; }

.author-box { display: flex; gap: 16px; align-items: flex-start; margin-top: 28px; padding: 20px; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); }
.author-box p { margin: 4px 0 0; color: var(--text-2); font-size: .94rem; }

.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin-top: 28px; }
.pager a { display: block; padding: 16px 18px; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); font-weight: 600; line-height: 1.4; }
.pager a:hover { border-color: var(--accent); }
.pager span { display: block; font-size: .78rem; color: var(--muted); font-weight: 500; margin-bottom: 4px; }
.pager .next { text-align: right; }

.article-layout .sidebar { position: sticky; top: 124px; align-self: start; }

/* ---------- 404 ---------- */
.notfound { text-align: center; padding-block: 72px 96px; display: flex; flex-direction: column; align-items: center; gap: 12px; }
.notfound p { color: var(--muted); max-width: 520px; margin: 0; }
.big-404 { font-size: clamp(5rem, 18vw, 9rem) !important; font-weight: 800; line-height: 1; color: var(--accent) !important; }
.notfound .search-form { width: 100%; margin-block: 12px; }

/* ---------- Footer ---------- */
.site-footer { background: var(--header); color: #aeb3bd; margin-top: 0; }
.footer-grid { display: grid; grid-template-columns: 1.6fr 1fr 1.4fr 1fr; gap: 36px; padding-block: 48px; }
.footer-about p { font-size: .92rem; margin: 14px 0 0; max-width: 340px; }
.site-footer h3 { color: #fff; font-size: .82rem; text-transform: uppercase; letter-spacing: .08em; margin-bottom: 14px; }
.site-footer ul { list-style: none; margin: 0; padding: 0; }
.site-footer li { padding: 5px 0; font-size: .92rem; line-height: 1.45; }
.site-footer a:hover { color: #fff; }
.footer-bottom { border-top: 1px solid rgba(255, 255, 255, .08); padding-block: 18px; font-size: .85rem; }

.to-top {
  position: fixed; right: 20px; bottom: 20px; width: 44px; height: 44px; border-radius: 50%;
  border: 0; background: var(--accent); color: #fff; display: grid; place-items: center;
  box-shadow: var(--shadow); opacity: 0; pointer-events: none; transform: translateY(10px); transition: .25s;
}
.to-top.show { opacity: 1; pointer-events: auto; transform: none; }

/* ---------- Responsive ---------- */
@media (max-width: 1080px) {
  .layout { grid-template-columns: 1fr; }
  .article-layout .sidebar { position: static; }
  .sidebar { display: grid; grid-template-columns: repeat(2, 1fr); gap: 20px; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 900px) {
  .burger { display: inline-grid; margin-left: -8px; }
  .topbar-inner { gap: 10px; }
  .main-nav {
    position: absolute; left: 0; right: 0; top: 64px; background: var(--header);
    border-top: 1px solid rgba(255, 255, 255, .08); display: none; padding: 8px 12px 16px;
  }
  .main-nav.open { display: block; }
  .main-nav ul { flex-direction: column; }
  .main-nav a { padding: 12px; font-size: 1rem; }
  .main-nav a.active::after { left: 0; right: auto; top: 10px; bottom: 10px; width: 3px; height: auto; border-radius: 0 3px 3px 0; }
  .hero { grid-template-columns: 1fr; }
  .hero-side { grid-template-columns: 1fr 1fr; grid-template-rows: none; }
  .card-overlay.big { min-height: 380px; }
  .cat-blocks, .card-grid { grid-template-columns: 1fr 1fr; }
  .cat-blocks .cat-block:last-child { grid-column: 1 / -1; }
}
@media (max-width: 640px) {
  .container { padding-inline: 16px; }
  .hero { margin-top: 16px; gap: 12px; }
  .hero-side { grid-template-columns: 1fr; gap: 12px; }
  .card-overlay.big { min-height: 320px; }
  .card-overlay.big .card-overlay-body { padding: 20px; }
  .card-overlay.big p { display: none; }
  .post-row { grid-template-columns: 120px minmax(0, 1fr); gap: 14px; padding-block: 16px; }
  .post-row h3 { font-size: 1.02rem; margin: 2px 0 6px; }
  .post-row p, .post-row .meta .by { display: none; }
  .post-row .kicker { font-size: .68rem; }
  .sidebar, .cat-blocks, .card-grid { grid-template-columns: 1fr; }
  .cat-blocks .cat-block:last-child { grid-column: auto; }
  .prose { font-size: 1rem; }
  .prose h2 { font-size: 1.35rem; }
  .pager { grid-template-columns: 1fr; }
  .pager .next { text-align: left; }
  .footer-grid { grid-template-columns: 1fr; gap: 24px; }
  .search-panel { top: 104px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  * { transition: none !important; }
}