/* Trang chủ */
.hero { position: relative; overflow: hidden; padding: 72px 0 64px; border-bottom: 1px solid var(--line); }
.hero::before {
  content: ""; position: absolute; inset: -30% -15% auto auto; width: 640px; height: 640px; border-radius: 50%;
  background: radial-gradient(closest-side, color-mix(in srgb, var(--lime) 38%, transparent), transparent); z-index: -1; pointer-events: none;
}
.hero-grid { display: grid; grid-template-columns: 1.05fr .95fr; gap: 56px; align-items: center; }
.eyebrow { display: inline-flex; align-items: center; gap: 8px; padding: 4px 12px; border-radius: 999px; border: 1px solid var(--line-strong); background: var(--surface); color: var(--ink-2); font-weight: 500; font-size: .82rem; margin-bottom: 20px; }
.eyebrow .dot { color: var(--ok); }
.hero h1 { font-size: clamp(2rem, 4.4vw, 3.1rem); font-weight: 800; letter-spacing: -.03em; line-height: 1.12; margin-bottom: 18px; }
.hero .lead { font-size: 1.1rem; color: var(--ink-2); max-width: 540px; margin-bottom: 28px; }
.hero-cta { display: flex; gap: 10px; flex-wrap: wrap; margin-bottom: 28px; }
.hero .checks { font-size: .94rem; }
/* Dòng "13 khóa học · … câu hỏi" với dãy ảnh khóa học chồng nhau */
.hero-proof { display: inline-flex; align-items: center; gap: 12px; margin-top: 26px; color: var(--ink-2); font-size: .9rem; text-decoration: none !important; }
.hero-proof b { color: var(--ink); }
.hero-proof:hover b { text-decoration: underline; text-underline-offset: 3px; }
.stack-thumbs { display: inline-flex; flex: none; }
.stack-thumbs .mono { border-radius: 50%; border: 2px solid var(--bg); box-shadow: none; width: 36px; height: 36px; }
.stack-thumbs .mono + .mono { margin-left: -10px; }

/* Khảm ảnh khóa học bên phải, thẻ câu hỏi mẫu đè lên phía trái */
.hero-visual { position: relative; padding: 36px 0; }
.hero-pics { position: absolute; top: 0; bottom: 0; right: -8px; width: 60%; display: grid; grid-template-columns: 1fr 1fr; grid-template-rows: repeat(6, 1fr); gap: 10px; pointer-events: none; }
.hero-pic { border-radius: 14px; overflow: hidden; background: var(--surface-2); box-shadow: var(--shadow-sm); }
.hero-pic:nth-child(1) { grid-column: 1; grid-row: 1 / 4; }
.hero-pic:nth-child(2) { grid-column: 2; grid-row: 1 / 3; }
.hero-pic:nth-child(3) { grid-column: 2; grid-row: 3 / 7; }
.hero-pic:nth-child(4) { grid-column: 1; grid-row: 4 / 7; }
.hero-visual .demo { width: 80%; }
.hero-visual .demo { position: relative; z-index: 1; }

/* Ví dụ một câu hỏi */
.demo { padding: 22px; box-shadow: var(--shadow); }
.demo-top { display: flex; justify-content: space-between; align-items: center; gap: 10px; margin-bottom: 14px; }
.demo-q { font-weight: 600; margin-bottom: 14px; }
.demo-opt { display: flex; gap: 12px; align-items: flex-start; padding: 10px 14px; border: 1px solid var(--line-strong); border-radius: 10px; margin-bottom: 8px; font-size: .92rem; background: var(--surface); }
.demo-opt .L { flex: none; width: 24px; height: 24px; border-radius: 6px; display: grid; place-items: center; font-weight: 700; font-size: .78rem; background: var(--surface-2); color: var(--ink-2); }
.demo-opt.ok { border-color: var(--ok); background: var(--ok-bg); }
.demo-opt.ok .L { background: var(--ok); color: #fff; }
.demo-opt.bad { border-color: var(--bad); background: var(--bad-bg); }
.demo-opt.bad .L { background: var(--bad); color: #fff; }
.demo-explain { margin-top: 12px; padding: 12px 14px; border-radius: 10px; background: var(--surface-2); font-size: .88rem; color: var(--ink-2); }
.demo-explain b { display: block; color: var(--ink); margin-bottom: 2px; }

.section { padding: 80px 0; }
.section-alt { background: var(--surface); border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.section-head { max-width: 640px; margin: 0 0 36px; }
.section-head.center { margin-inline: auto; text-align: center; }
.section-head h2 { font-size: clamp(1.5rem, 3vw, 2.1rem); font-weight: 800; letter-spacing: -.025em; }
.section-head p { color: var(--ink-2); font-size: 1.02rem; margin: 0; }
.kicker { display: block; color: var(--muted); font-weight: 600; font-size: .8rem; letter-spacing: .06em; text-transform: uppercase; margin-bottom: 10px; }

/* Danh mục bộ đề: tìm kiếm, lọc, phân trang */
.catalog { scroll-margin-top: calc(var(--header-h) + 16px); }
.cat-toolbar { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; margin-bottom: 12px; }
.cat-search { flex: 1 1 320px; display: flex; align-items: center; gap: 10px; padding: 0 6px 0 14px; min-height: 44px; border-radius: 10px; border: 1px solid var(--line-strong); background: var(--surface); cursor: text; transition: border-color .15s, box-shadow .15s; }
.cat-search:focus-within { border-color: var(--brand); box-shadow: var(--ring); }
.cat-search > .i { color: var(--muted); }
.cat-search input { flex: 1; min-width: 0; border: 0; outline: 0; background: transparent; padding: 8px 0; font-size: .96rem; }
.cat-search input::-webkit-search-cancel-button { display: none; }
.cat-clear { width: 32px; height: 32px; border-radius: 8px; border: 0; background: transparent; color: var(--muted); cursor: pointer; flex: none; display: grid; place-items: center; }
.cat-clear:hover { background: var(--surface-2); color: var(--ink); }
.cat-controls { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }
select.input.cat-sort { width: auto; min-height: 44px; font-weight: 500; font-size: .9rem; }
/* Ô danh mục: ảnh đại diện (ảnh khóa đầu tiên của danh mục) + tên + số khóa */
.cat-tiles { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 16px; }
.cat-tile { display: inline-flex; align-items: center; gap: 10px; padding: 6px 14px 6px 6px; border-radius: 12px; border: 1px solid var(--line-strong); background: var(--surface);
  color: var(--ink); cursor: pointer; text-align: left; transition: border-color .15s, background-color .15s, box-shadow .15s; }
.cat-tile:hover { border-color: var(--muted); box-shadow: var(--shadow-sm); }
.cat-tile .mono { flex: none; }
.cat-tile .cat-all { background: var(--surface-2); color: var(--ink-2); }
.cat-tile .cat-all .i { width: 18px; height: 18px; }
.cat-tile-txt { display: grid; line-height: 1.25; }
.cat-tile-txt b { font-size: .88rem; font-weight: 600; white-space: nowrap; }
.cat-tile-txt small { font-size: .74rem; color: var(--muted); }
.cat-tile.is-empty { opacity: .5; }   /* không còn khóa nào khớp từ khóa / giá: giữ chỗ để hàng ô không nhảy */
.cat-tile[aria-pressed="true"] { background: var(--brand); border-color: var(--brand); color: var(--on-brand); }
.cat-tile[aria-pressed="true"] small { color: color-mix(in srgb, var(--on-brand) 75%, transparent); }
.cat-tile[aria-pressed="true"] .cat-all { background: color-mix(in srgb, var(--on-brand) 16%, transparent); color: var(--on-brand); }
.cat-summary { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; min-height: 26px; margin-bottom: 16px; color: var(--muted); font-size: .9rem; }
.cat-summary b { color: var(--ink); font-weight: 600; }
.cat-more { margin-top: 28px; text-align: center; color: var(--muted); font-size: .92rem; }
#pkgPager .pager { margin-top: 16px; }
/* Đang tải trang khóa học: làm mờ nội dung cũ thay vì nháy trắng */
#pkgGrid { transition: opacity .15s; }
#pkgGrid[aria-busy="true"]:not(:has(.skel, .spinner)) { opacity: .55; pointer-events: none; }

/* Lưới khóa học: thẻ có ảnh bìa 16:10 */
.course-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(290px, 1fr)); gap: 20px; }
.course-card { display: flex; flex-direction: column; overflow: hidden; color: inherit; text-decoration: none !important; transition: border-color .2s, box-shadow .2s, transform .2s; }
.course-card:hover { border-color: var(--line-strong); box-shadow: var(--shadow); transform: translateY(-2px); }
.course-card:focus-visible { outline: none; box-shadow: var(--ring); }
.course-media { position: relative; aspect-ratio: 16 / 10; overflow: hidden; background: var(--surface-2); }
.course-media .cover { transition: transform .5s ease; }
.course-card:hover .course-media .cover { transform: scale(1.04); }
.course-media::after { content: ""; position: absolute; inset: auto 0 0; height: 45%; background: linear-gradient(transparent, rgba(10, 12, 6, .45)); pointer-events: none; }
.course-tags { position: absolute; top: 12px; left: 12px; right: 12px; display: flex; gap: 6px; flex-wrap: wrap; z-index: 1; }
.course-tags .badge { box-shadow: 0 1px 4px rgba(0, 0, 0, .18); }
.course-tags .badge-green { background: #e6f5ea; }
.course-code { position: absolute; left: 12px; bottom: 10px; z-index: 1; color: #fff; font-weight: 700; font-size: .74rem; letter-spacing: .06em;
  padding: 2px 8px; border-radius: 6px; background: rgba(12, 16, 6, .45); backdrop-filter: blur(4px); -webkit-backdrop-filter: blur(4px); }
.course-body { display: flex; flex-direction: column; gap: 8px; padding: 16px 18px 18px; flex: 1; }
.course-body h3 { font-size: 1.08rem; margin: 0; color: var(--ink); letter-spacing: -.015em; }
.course-body p { color: var(--ink-2); font-size: .89rem; line-height: 1.5; margin: 0; display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }
.course-meta { display: flex; flex-wrap: wrap; gap: 4px 14px; color: var(--muted); font-size: .82rem; }
.course-meta span { display: inline-flex; align-items: center; gap: 5px; }
.course-meta .i { width: 15px; height: 15px; }
.course-match { align-self: flex-start; font-size: .78rem; font-weight: 600; color: var(--brand-600); background: var(--brand-50); padding: 2px 8px; border-radius: 6px; }
.course-foot { margin-top: auto; display: flex; align-items: center; justify-content: space-between; gap: 12px; padding-top: 12px; border-top: 1px solid var(--line); }
.course-price { display: flex; align-items: baseline; gap: 4px; flex-wrap: wrap; }
.course-price .per { color: var(--muted); font-size: .82rem; }
.course-owned { display: inline-flex; align-items: center; gap: 6px; color: var(--ok); font-weight: 600; font-size: .9rem; }
.course-card.skel .course-media { animation: skel 1.2s ease-in-out infinite alternate; }
.course-card.skel .course-body { gap: 10px; }

/* Trang một khóa học (?subject=): đầu trang ảnh + giới thiệu, rồi danh sách bộ đề */
.course-hero { display: grid; grid-template-columns: minmax(0, 1.05fr) minmax(0, 1fr); overflow: hidden; margin-bottom: 28px; }
.course-hero-media { position: relative; min-height: 280px; background: var(--surface-2); }
.course-hero-media .cover { position: absolute; inset: 0; }
.course-hero-body { padding: 26px 30px 28px; display: flex; flex-direction: column; gap: 10px; justify-content: center; }
.course-back { align-self: flex-start; font-size: .88rem; color: var(--muted); margin-bottom: 4px; }
.course-back:hover { color: var(--ink); }
.course-hero-body h3 { font-size: clamp(1.4rem, 2.6vw, 1.9rem); font-weight: 800; letter-spacing: -.025em; margin: 0; }
.course-hero-body > p { color: var(--ink-2); margin: 0; }
.course-facts { list-style: none; margin: 4px 0 6px; padding: 0; display: flex; flex-wrap: wrap; gap: 8px; }
.course-facts li { display: inline-flex; align-items: baseline; gap: 4px; padding: 5px 10px; border-radius: 8px; background: var(--surface-2); color: var(--ink-2); font-size: .85rem; }
.course-facts li b { color: var(--ink); }
.course-facts .price { font-size: .95rem; }
.course-facts .per { color: var(--muted); font-size: .8rem; }
.course-hero .hero-cta { margin: 6px 0 0; }
/* Danh sách bộ đề của khóa: một bảng mục lục, cột thẳng hàng (số · tên · số câu · tiến độ · giá · nút) */
.chap-head { display: flex; align-items: flex-end; justify-content: space-between; gap: 12px 24px; flex-wrap: wrap; margin-bottom: 14px; }
.chap-head h3 { font-size: 1.25rem; font-weight: 800; letter-spacing: -.02em; margin: 0 0 2px; }
.chap-head p { margin: 0; color: var(--muted); font-size: .9rem; }
.chap-search { flex: 0 1 300px; display: flex; align-items: center; gap: 8px; padding: 0 12px; min-height: 40px; border-radius: 10px; border: 1px solid var(--line-strong); background: var(--surface); cursor: text; transition: border-color .15s, box-shadow .15s; }
.chap-search:focus-within { border-color: var(--brand); box-shadow: var(--ring); }
.chap-search > .i { color: var(--muted); width: 17px; height: 17px; }
.chap-search input { flex: 1; min-width: 0; border: 0; outline: 0; background: transparent; padding: 6px 0; font-size: .92rem; }
.chap-tools { display: flex; align-items: center; justify-content: space-between; gap: 10px 20px; flex-wrap: wrap; margin-bottom: 14px; }
.chap-filter { max-width: 100%; overflow-x: auto; scrollbar-width: none; }
.chap-filter::-webkit-scrollbar { display: none; }
.chap-meter { display: flex; align-items: center; gap: 10px; margin-left: auto; font-size: .84rem; color: var(--muted); }
.chap-meter .chap-bar { width: 140px; }
.chap-meter b { color: var(--ink); font-variant-numeric: tabular-nums; min-width: 3ch; text-align: right; }
.chap-bar { display: block; height: 6px; border-radius: 99px; background: var(--line); overflow: hidden; }
.chap-bar i { display: block; height: 100%; border-radius: inherit; background: var(--brand); }

.chap-panel { overflow: hidden; }
.chap-thead, .chap-row { display: grid; grid-template-columns: var(--chap-cols); column-gap: 18px; align-items: center; padding-inline: 20px; }
.chap-thead { padding-block: 10px; background: var(--surface-2); border-bottom: 1px solid var(--line); color: var(--muted); font-size: .7rem; font-weight: 600; letter-spacing: .07em; text-transform: uppercase; }
.chap-list { list-style: none; margin: 0; padding: 0; }
.chap-row { position: relative; padding-block: 14px; min-height: 68px; transition: background-color .15s; }
.chap-row + .chap-row { border-top: 1px solid var(--line); }
.chap-row:hover { background: color-mix(in srgb, var(--surface-2) 70%, var(--surface)); }
.chap-cells { display: contents; }
.chap-idx { width: 36px; height: 36px; border-radius: 10px; display: grid; place-items: center; background: var(--surface-2); color: var(--ink-2); font-weight: 700; font-size: .86rem; font-variant-numeric: tabular-nums; }
.chap-idx.wide { width: auto; min-width: 36px; padding: 0 8px; font-size: .74rem; white-space: nowrap; }
.chap-idx .i { width: 18px; height: 18px; stroke-width: 2.4; }
.chap-row.is-learning .chap-idx { background: var(--brand-50); color: var(--brand-600); box-shadow: inset 0 0 0 1.5px color-mix(in srgb, var(--brand) 35%, transparent); }
.chap-row.is-done .chap-idx { background: var(--ok-bg); color: var(--ok); }
.chap-main { min-width: 0; display: flex; flex-wrap: wrap; align-items: center; gap: 4px 10px; }
.chap-main h4 { font-size: .98rem; font-weight: 600; line-height: 1.4; margin: 0; color: var(--ink); }
/* Cả dòng bấm được (mở trang chi tiết bộ đề); nút "Học" nằm trên lớp đó */
.chap-link { color: inherit; text-decoration: none !important; }
.chap-link::after { content: ""; position: absolute; inset: 0; }
.chap-link:focus-visible { outline: none; }
.chap-link:focus-visible::after { box-shadow: inset 0 0 0 2px var(--brand); }
.chap-row:hover .chap-link { color: var(--brand-600); }
.chap-kicker { color: var(--muted); font-weight: 500; margin-right: .4em; }
.chap-kicker::after { content: " ·"; }
.chap-flag { font-size: .66rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; padding: 1px 7px; border-radius: 5px; background: var(--lime); color: var(--olive); }
.chap-count { color: var(--muted); font-size: .86rem; white-space: nowrap; }
.chap-count b { color: var(--ink); font-weight: 600; font-variant-numeric: tabular-nums; }
.chap-count small, .chap-price small { display: block; font-size: .74rem; line-height: 1.3; }
.chap-prog { display: grid; gap: 5px; min-width: 0; }
.chap-prog small { color: var(--muted); font-size: .76rem; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.chap-row.is-done .chap-bar i { background: var(--ok); }
.chap-price { white-space: nowrap; }
.chap-price .price { font-size: .98rem; }
.chap-price small { color: var(--muted); }
.chap-price .badge .i { width: 13px; height: 13px; stroke-width: 2.4; }
.chap-go { position: relative; z-index: 1; justify-self: end; }
.chap-go .i { transition: transform .15s; }
.chap-go:hover .i { transform: translateX(2px); }
/* Bộ nên học tiếp: viền nhấn bên trái + nút đậm */
.chap-row.is-next { background: color-mix(in srgb, var(--brand-50) 55%, var(--surface)); box-shadow: inset 3px 0 0 var(--brand); }
.chap-none { padding: 32px 16px; }

@media (max-width: 760px) {
  .course-hero { grid-template-columns: 1fr; }
  .course-hero-media { min-height: 0; aspect-ratio: 16 / 9; }
  .course-hero-body { padding: 20px; }
  .course-hero .hero-cta .btn { flex: 1 1 auto; }
}
@media (max-width: 720px) {
  .cat-search kbd { display: none; }
  .cat-controls { width: 100%; }
  .seg { flex: 1; }
  .seg button { flex: 1; padding: 6px 8px; }
  .cat-sort { flex: 1 1 100%; }
  /* Ô danh mục cuộn ngang trên điện thoại thay vì xuống nhiều dòng */
  .cat-tiles { flex-wrap: nowrap; overflow-x: auto; margin: 0 -16px 14px; padding: 2px 16px 6px; scrollbar-width: none; }
  .cat-tiles::-webkit-scrollbar { display: none; }
  .cat-tile { flex: none; }
  .course-grid { grid-template-columns: 1fr; gap: 16px; }
  /* Điện thoại: số · (tên / số câu · giá / thanh tiến độ) · nút */
  .chap-head { align-items: stretch; }
  .chap-search { flex: 1 1 100%; }
  .chap-meter { margin-left: 0; flex: 1 1 100%; }
  .chap-meter .chap-bar { flex: 1; width: auto; }
  .chap-thead { display: none; }
  .chap-row { grid-template-columns: auto minmax(0, 1fr) auto; grid-template-areas: "idx main go" "idx cells go"; column-gap: 12px; row-gap: 4px; padding: 12px 14px; }
  .chap-idx { grid-area: idx; align-self: start; }
  .chap-main { grid-area: main; }
  .chap-cells { grid-area: cells; display: flex; flex-wrap: wrap; align-items: center; gap: 4px 10px; }
  .chap-count small, .chap-price small { display: inline; margin-left: 4px; }
  .chap-count small::before, .chap-price small::before { content: "· "; }
  .chap-price .price { font-size: .86rem; }
  .chap-prog { order: 3; flex: 1 1 100%; grid-template-columns: minmax(60px, 1fr) auto; align-items: center; gap: 10px; }
  .chap-prog:empty { display: none; }
  .chap-go { grid-area: go; }
}
@media (max-width: 480px) {
  .chap-go { width: 36px; padding: 0; border-radius: 50%; }
  .chap-go-t { display: none; }
}
@media (prefers-reduced-motion: reduce) { .course-card, .course-media .cover { transition: none; } .course-card:hover, .course-card:hover .course-media .cover { transform: none; } }

/* Tính năng */
.feature-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1px; background: var(--line); border: 1px solid var(--line); border-radius: var(--r-lg); overflow: hidden; }
.feature { padding: 26px 24px; background: var(--surface); }
.feature h3 { font-size: 1rem; margin-bottom: 6px; }
.feature p { color: var(--ink-2); font-size: .93rem; margin: 0; }

/* Các bước */
.steps { display: grid; grid-template-columns: repeat(4, 1fr); gap: 16px; counter-reset: step; }
.step { padding: 24px 22px; }
.step::before { counter-increment: step; content: counter(step, decimal-leading-zero); display: block; font-weight: 700; font-size: .85rem; color: var(--muted); letter-spacing: .04em; margin-bottom: 18px; }
.step h3 { font-size: 1rem; }
.step p { color: var(--ink-2); font-size: .92rem; margin: 0; }

/* Bảng giá */
.pricing { display: grid; grid-template-columns: 1.1fr .9fr; gap: 20px; align-items: stretch; }
.price-card { padding: 32px; border: 1.5px solid var(--olive); }
:root[data-theme="dark"] .price-card { border-color: var(--lime); }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .price-card { border-color: var(--lime); } }
.price-card .big { font-size: 2.5rem; font-weight: 800; letter-spacing: -.03em; }
.price-card .checks { margin: 22px 0 26px; }
.compare { padding: 32px; background: var(--surface-2); }
.compare h3 { font-size: 1rem; margin-bottom: 8px; }
.compare-row { display: flex; justify-content: space-between; gap: 16px; padding: 13px 0; border-bottom: 1px solid var(--line-strong); font-size: .93rem; color: var(--ink-2); }
.compare-row:last-child { border-bottom: none; color: var(--ink); font-weight: 600; }

/* Hỏi đáp */
.faq { max-width: 780px; margin: 0 auto; border-top: 1px solid var(--line); }
.faq details { border-bottom: 1px solid var(--line); }
.faq summary { cursor: pointer; padding: 18px 0; font-weight: 600; list-style: none; display: flex; justify-content: space-between; align-items: center; gap: 16px; }
.faq summary::-webkit-details-marker { display: none; }
.faq summary .i { color: var(--muted); transition: transform .2s; }
.faq details[open] summary .i { transform: rotate(180deg); }
.faq details p { color: var(--ink-2); margin: -4px 0 18px; max-width: 680px; }

.cta-band { border-radius: 20px; padding: 56px 32px; text-align: center; color: #fff; background: var(--olive); }
.cta-band h2 { color: var(--lime); font-size: clamp(1.5rem, 3vw, 2.1rem); font-weight: 800; letter-spacing: -.025em; }
.cta-band p { opacity: .85; font-size: 1.02rem; margin-bottom: 24px; }
:root[data-theme="dark"] .cta-band { background: var(--surface); border: 1px solid var(--line); }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .cta-band { background: var(--surface); border: 1px solid var(--line); } }

@media (max-width: 960px) {
  .hero-grid, .pricing { grid-template-columns: 1fr; }
  .hero-grid { gap: 40px; }
  .demo { max-width: 560px; }
  .hero-visual { max-width: 560px; }
  .hero-pics { display: none; }
  .hero-visual { padding: 0; }
  .hero-visual .demo { width: auto; }
  .steps { grid-template-columns: 1fr 1fr; }
  .feature-grid { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 640px) {
  .hero { padding: 44px 0 48px; }
  .feature-grid, .steps { grid-template-columns: 1fr; }
  .section { padding: 56px 0; }
  .hero-cta .btn { flex: 1; }
  .price-card, .compare { padding: 24px; }
}