html { font-size: 16px; }
body { color: #182235; font-family: Inter, system-ui, -apple-system, "Segoe UI", sans-serif; }
a { color: #0758c9; }
.hero { background: linear-gradient(120deg, #eef7ff 0%, #f7f3ff 100%); }
.hero-card { background: linear-gradient(145deg, #123d90, #6329a6); color: white; border-radius: 1.25rem; min-height: 260px; padding: 2rem; font-size: 1.35rem; box-shadow: 0 20px 45px rgba(18,61,144,.25); }
.hero-card span { display: block; font-weight: 800; font-size: 4.5rem; line-height: 1; opacity: .85; margin-bottom: 3rem; }
.content { max-width: 820px; }
.article p { font-size: 1.12rem; line-height: 1.8; }
.card { border-radius: .8rem; }
.navbar-brand { letter-spacing: .05em; }
.site-logo { display: block; max-width: 220px; height: 48px; object-fit: contain; }
.site-banner { display: block; width: 100%; max-height: 420px; object-fit: cover; }
.course-card-image, .article-card-image { display: block; width: 100%; height: 190px; object-fit: cover; }
.article-hero-image { display: block; width: 100%; max-height: 460px; object-fit: cover; border-radius: .75rem; }
.image-preview { height: 140px; padding: .5rem; border: 1px solid #dee2e6; border-radius: .5rem; background: #f8f9fa; }
.image-preview img { width: 100%; height: 100%; object-fit: contain; }
.zalo-floating { position: fixed; right: 24px; bottom: 28px; z-index: 1040; display: grid; place-items: center; width: 72px; height: 72px; border: 5px solid #fff; border-radius: 50%; background: #0866ff; color: #0866ff; text-decoration: none; box-shadow: 0 8px 24px rgba(0, 64, 160, .32); transition: transform .2s ease, box-shadow .2s ease; }
.zalo-floating::before { content: ""; position: absolute; inset: 8px; border-radius: 50%; background: #fff; }
.zalo-floating::after { content: ""; position: absolute; right: 5px; bottom: 4px; width: 18px; height: 18px; background: #fff; clip-path: polygon(0 0, 100% 0, 100% 100%); transform: rotate(12deg); }
.zalo-floating-label { position: relative; z-index: 1; font-size: 1.25rem; font-weight: 700; letter-spacing: -.04em; }
.zalo-floating:hover, .zalo-floating:focus-visible { color: #0758dc; transform: translateY(-3px) scale(1.04); box-shadow: 0 12px 30px rgba(0, 64, 160, .42); }
.admin-menu { position: sticky; top: 73px; z-index: 1010; background: rgba(255,255,255,.97); border-bottom: 1px solid #dee2e6; box-shadow: 0 .15rem .45rem rgba(0,0,0,.05); }
.admin-menu-scroll { display: flex; gap: .75rem; padding: 1rem 0; overflow-x: auto; white-space: nowrap; scrollbar-width: thin; }
.admin-menu .btn { flex: 0 0 auto; padding: .65rem 1.1rem; }
.admin-menu .btn.active { color: #fff; background-color: #0d6efd; border-color: #0d6efd; }
@media (max-width: 576px) {
    .display-4 { font-size: 2.35rem; }
    .admin-menu { top: 69px; }
    .zalo-floating { right: 16px; bottom: 18px; width: 64px; height: 64px; }
}