/* Hoc Cung Son — he thiet ke chung: mobile-first, chu to, nut to, chuyen nghiep. */
:root{--blue:#143a6b;--blue2:#1d6fd1;--yellow:#ffc107;--orange:#ff7a29;--green:#1a9e57;--red:#b42318;--bg:#eef3fb;--ink:#16233a;--muted:#5b6b85}
*{box-sizing:border-box}
body{font-family:system-ui,-apple-system,Arial,sans-serif;margin:0;background:var(--bg);color:var(--ink);font-size:19px;line-height:1.6}
a{color:var(--blue2);text-decoration:none}
.topbar{background:#fff;border-bottom:1px solid #e2e6ef;position:sticky;top:0;z-index:10}
.topbar-inner{max-width:1140px;margin:0 auto;padding:14px 18px;display:flex;gap:14px;align-items:center;flex-wrap:wrap}
.brand{font-weight:800;font-size:22px;color:var(--blue)}
.brand small{display:block;font-size:14px;color:var(--muted);font-weight:400}
.topbar nav{margin-left:auto;display:flex;gap:8px;flex-wrap:wrap}
.topbar nav a{padding:10px 14px;border-radius:999px;color:var(--ink)}
.topbar nav a.cta{background:var(--yellow);color:#222;font-weight:700}
.wrap{max-width:1140px;margin:0 auto;padding:18px}
.hero{background:linear-gradient(135deg,#0f2f5c,#1d6fd1);color:#fff;border-radius:24px;padding:32px}
.hero h1{font-size:40px;line-height:1.25;margin:0 0 10px}
.hero p{font-size:20px;opacity:.95}
.hero .btns{display:flex;gap:12px;flex-wrap:wrap;margin-top:18px}
.btn{display:inline-block;border:0;border-radius:14px;padding:15px 22px;background:var(--blue);color:#fff;cursor:pointer;font-size:19px;font-weight:700;min-height:56px;text-align:center}
.btn.y{background:var(--yellow);color:#222}.btn.o{background:var(--orange)}.btn.g{background:var(--green)}.btn.light{background:#fff;color:var(--blue)}
.btn.secondary{background:#e8edf5;color:var(--blue)}
.card{background:#fff;border:1px solid #e2e6ef;border-radius:20px;padding:22px;margin-bottom:16px;box-shadow:0 10px 22px rgba(20,58,107,.10)}
.grid{display:grid;grid-template-columns:repeat(3,1fr);gap:16px}
.grid2{display:grid;grid-template-columns:repeat(2,1fr);gap:16px}
@media(max-width:900px){.grid,.grid2{grid-template-columns:1fr}.hero h1{font-size:32px}}
.stat{font-size:34px;font-weight:800;color:var(--blue)}
.badge{display:inline-block;background:#e8f3ff;color:var(--blue);border-radius:999px;padding:6px 14px;font-size:16px;font-weight:700}
.badge.green{background:#e6f7ee;color:var(--green)}.badge.orange{background:#fff0e6;color:#c2570a}.badge.grey{background:#eef1f6;color:var(--muted)}
input,select,textarea{width:100%;padding:14px;border:1px solid #ccd3e0;border-radius:12px;margin:6px 0 12px;box-sizing:border-box;font-size:19px;min-height:56px;font-family:inherit}
label{font-weight:700}
.muted{color:var(--muted);font-size:17px}.bad{color:var(--red)}.ok{color:var(--green)}
.bar{height:16px;background:#e8edf5;border-radius:10px;overflow:hidden}.bar i{display:block;height:100%;background:linear-gradient(90deg,#1d6fd1,#1a9e57)}
.tabs{display:flex;gap:8px;flex-wrap:wrap;margin:14px 0}
.tabs button{background:#fff;color:var(--ink);border:1px solid #e2e6ef}
.tabs button.active{background:var(--blue);color:#fff}
.course{display:grid;grid-template-columns:1fr 340px;gap:16px;align-items:start}
@media(max-width:800px){.course{grid-template-columns:1fr}}
.lesson-btn{display:block;width:100%;text-align:left;background:#eef3fb;color:var(--blue);margin:4px 0}
.video-box{aspect-ratio:16/9;background:#111;color:#fff;display:grid;place-items:center;border-radius:16px;text-align:center;padding:16px}
.video-box iframe{width:100%;height:100%;border:0}
.q{border-top:1px solid #eee;padding:14px 0}
.q label{display:block;font-weight:400;margin:6px 0}
footer{background:#0f2f5c;color:#fff;margin-top:24px}
footer .wrap{padding:28px 18px}
footer a{color:#cfe3ff}
.student-head{display:flex;gap:16px;align-items:center;flex-wrap:wrap}
.avatar{width:72px;height:72px;border-radius:50%;background:linear-gradient(135deg,#1d6fd1,#ffc107);display:grid;place-items:center;font-size:32px;font-weight:800;color:#fff}
.table{width:100%;border-collapse:collapse;font-size:18px}
.table th,.table td{padding:12px;border-bottom:1px solid #eef1f6;text-align:left}
@media(max-width:700px){.table{font-size:16px}}