/* Hệ thống giao diện dùng chung cho danh mục khóa học, thanh toán và trang học */
:root{
  --bg:#0D1C19; --bg-deep:#091512;
  --surface:#122822; --surface-2:#16352C;
  --border:rgba(198,255,230,.12); --border-strong:rgba(62,240,177,.40);
  --mint:#3EF0B1; --mint-hover:#67F5C5; --mint-soft:#A9F4D1; --cyan:#56DCC8;
  --cta-text:#07130F;
  --heading:#F4FBF8; --body:#D6E5DF; --muted:#A4B8B0; --caption:#829A91;
  --warn:#FFC978; --danger:#FF8E8E;
  --radius-card:20px; --radius-btn:13px;
  --font:"DM Sans",system-ui,sans-serif;
}
*{margin:0;padding:0;box-sizing:border-box}
html{scroll-behavior:smooth}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*::before,*::after{animation:none!important;transition:none!important}}
body{font-family:var(--font);font-size:16px;line-height:24px;background:var(--bg);color:var(--body);-webkit-font-smoothing:antialiased;overflow-x:hidden}
img,svg{display:block;max-width:100%}
a{color:inherit}
button{font:inherit;cursor:pointer;background:none;border:none;color:inherit}
input,textarea,select{font:inherit;color:var(--heading)}
:focus-visible{outline:2px solid var(--mint);outline-offset:3px;border-radius:4px}
[hidden]{display:none!important}
.ic{width:24px;height:24px;stroke:currentColor;stroke-width:2;stroke-linecap:round;stroke-linejoin:round;fill:none;flex:none}
.ic-sm{width:18px;height:18px}

.container{max-width:1160px;margin:0 auto;padding:0 18px}
@media(min-width:768px){.container{padding:0 24px}}
@media(min-width:1024px){.container{padding:0 32px}}
.section{padding:56px 0 80px}
@media(min-width:1024px){.section{padding:72px 0 110px}}

h1,h2,h3,h4{color:var(--heading);font-weight:600}
h1{font-size:clamp(30px,6vw,42px);line-height:1.12;letter-spacing:-.02em}
h2{font-size:clamp(24px,4vw,32px);line-height:1.2}
h3{font-size:19px;line-height:1.3}
.lead{font-size:16px;line-height:25px;color:var(--muted);max-width:66ch}
.caption{font-size:14px;line-height:20px;color:var(--caption)}
.mint{color:var(--mint)}
.eyebrow{display:inline-flex;align-items:center;gap:8px;font-size:13px;font-weight:600;letter-spacing:.08em;text-transform:uppercase;color:var(--mint);background:rgba(62,240,177,.08);border:1px solid var(--border);padding:6px 14px;border-radius:100px;margin-bottom:18px}

.skip-link{position:absolute;left:16px;top:-60px;z-index:200;background:var(--mint);color:var(--cta-text);font-weight:600;padding:12px 20px;border-radius:12px;text-decoration:none;transition:top .2s}
.skip-link:focus{top:16px}

/* Nút */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;font-size:16px;font-weight:600;line-height:1;min-height:50px;padding:0 24px;border-radius:var(--radius-btn);text-decoration:none;transition:background-color .2s,box-shadow .2s,border-color .2s,opacity .2s}
.btn-primary{background:var(--mint);color:var(--cta-text)}
.btn-primary:hover{background:var(--mint-hover);box-shadow:0 6px 22px rgba(62,240,177,.25)}
.btn-primary:disabled{opacity:.5;cursor:not-allowed;box-shadow:none}
.btn-secondary{background:transparent;color:var(--heading);border:1px solid var(--border-strong)}
.btn-secondary:hover{background:rgba(62,240,177,.08);border-color:var(--mint)}
.btn-sm{min-height:42px;padding:0 18px;font-size:14px;border-radius:11px}
.btn-block{width:100%}

/* Thanh điều hướng */
.topbar{position:sticky;top:0;z-index:50;background:rgba(9,21,18,.9);backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);border-bottom:1px solid var(--border)}
.topbar .container{display:flex;align-items:center;justify-content:space-between;gap:16px;padding-top:12px;padding-bottom:12px}
.brand{display:flex;align-items:center;gap:12px;text-decoration:none;min-height:44px}
.brand-mark{width:40px;height:40px;border-radius:12px;background:var(--surface-2);border:1px solid var(--border-strong);display:flex;align-items:center;justify-content:center;color:var(--mint);flex:none}
.brand-name{font-weight:700;color:var(--heading);font-size:16px;line-height:1.2;display:block}
.brand-sub{font-size:12px;line-height:1.3;color:var(--caption)}
.topbar nav{display:flex;align-items:center;gap:8px}
.topbar nav a{display:inline-flex;align-items:center;min-height:44px;padding:0 12px;border-radius:10px;font-size:14px;font-weight:500;color:var(--body);text-decoration:none}
.topbar nav a:hover{color:var(--mint);background:rgba(62,240,177,.06)}

/* Thẻ */
.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius-card);padding:24px}

/* Danh mục khóa học */
.course-grid{display:grid;gap:20px}
@media(min-width:640px){.course-grid{grid-template-columns:repeat(2,1fr)}}
@media(min-width:1024px){.course-grid{grid-template-columns:repeat(3,1fr)}}
.course-card{display:flex;flex-direction:column;background:var(--surface);border:1px solid var(--border);border-radius:var(--radius-card);overflow:hidden;transition:border-color .2s,transform .2s}
.course-card:hover{border-color:var(--border-strong)}
.course-thumb{position:relative;aspect-ratio:16/9;background:var(--bg-deep);border-bottom:1px solid var(--border);display:flex;align-items:center;justify-content:center;overflow:hidden}
.course-thumb img{width:100%;height:100%;object-fit:cover}
.course-thumb .ph{display:flex;flex-direction:column;align-items:center;gap:8px;color:var(--caption);font-size:12px}
.course-thumb .ph .ic{width:28px;height:28px;color:var(--border-strong)}
.course-body{padding:22px;display:flex;flex-direction:column;flex:1}
.course-body h3{margin-bottom:6px}
.course-body .sub{font-size:14px;line-height:20px;color:var(--muted);margin-bottom:16px}
.price-row{display:flex;align-items:baseline;gap:10px;flex-wrap:wrap;margin-top:auto;margin-bottom:16px}
.price-now{font-size:24px;font-weight:700;color:var(--mint)}
.price-old{font-size:15px;color:var(--caption);text-decoration:line-through}
.course-body .btn{width:100%}

/* Biểu mẫu */
.field{margin-bottom:16px}
.field label{display:block;font-size:13px;font-weight:600;color:var(--mint-soft);margin-bottom:6px}
.field .req{color:var(--mint)}
.input{width:100%;background:var(--bg-deep);border:1px solid var(--border);border-radius:12px;padding:12px 14px;min-height:48px;transition:border-color .2s}
.input:focus{border-color:var(--border-strong);outline:none}
.field-help{font-size:12px;color:var(--caption);margin-top:6px;line-height:17px}

/* Thông báo */
.alert{display:flex;gap:10px;align-items:flex-start;border-radius:12px;padding:12px 14px;font-size:14px;line-height:20px;margin-bottom:16px}
.alert .ic{width:18px;height:18px;margin-top:1px;flex:none}
.alert-err{background:rgba(255,142,142,.08);border:1px solid rgba(255,142,142,.35);color:var(--danger)}
.alert-warn{background:rgba(255,201,120,.08);border:1px solid rgba(255,201,120,.35);color:var(--warn)}
.alert-ok{background:rgba(62,240,177,.08);border:1px solid var(--border-strong);color:var(--mint-soft)}

/* Thanh toán */
.pay-grid{display:grid;gap:22px;align-items:start}
@media(min-width:900px){.pay-grid{grid-template-columns:1fr 1fr}}
.qr-box{background:#fff;border-radius:16px;padding:14px;width:100%;max-width:260px;margin:0 auto 18px}
.qr-box img{width:100%;height:auto;display:block}
.qr-skeleton{aspect-ratio:1;display:flex;align-items:center;justify-content:center;color:#0E221C;font-size:13px;text-align:center;padding:12px}
.pay-rows{display:flex;flex-direction:column;gap:2px;margin-bottom:18px}
.pay-row{display:flex;justify-content:space-between;align-items:center;gap:12px;padding:12px 0;border-bottom:1px solid var(--border)}
.pay-row:last-child{border-bottom:none}
.pay-row .k{font-size:14px;color:var(--muted);flex:none}
.pay-row .v{font-weight:600;color:var(--heading);text-align:right;word-break:break-word}
.pay-row .v.big{font-size:19px;color:var(--mint)}
.copy-btn{display:inline-flex;align-items:center;gap:6px;font-size:12px;font-weight:600;color:var(--mint);background:rgba(62,240,177,.08);border:1px solid var(--border);border-radius:8px;padding:5px 10px;min-height:32px;margin-left:8px}
.copy-btn:hover{border-color:var(--border-strong)}
.status-box{display:flex;gap:12px;align-items:center;background:var(--surface-2);border:1px solid var(--border-strong);border-radius:14px;padding:16px;margin-top:6px}
.spin{width:18px;height:18px;border:2px solid rgba(62,240,177,.25);border-top-color:var(--mint);border-radius:50%;animation:sp .8s linear infinite;flex:none}
@keyframes sp{to{transform:rotate(360deg)}}
.steps{list-style:none;counter-reset:s;display:flex;flex-direction:column;gap:12px;margin-top:4px}
.steps li{counter-increment:s;display:flex;gap:12px;font-size:14px;line-height:21px;color:var(--body)}
.steps li::before{content:counter(s);flex:none;width:24px;height:24px;border-radius:50%;background:var(--surface-2);border:1px solid var(--border-strong);color:var(--mint);font-size:12px;font-weight:700;display:flex;align-items:center;justify-content:center}

/* Trang học */
.learn-layout{display:grid;gap:24px;align-items:start}
@media(min-width:1000px){.learn-layout{grid-template-columns:1fr 340px}}
.player-wrap{background:#000;border:1px solid var(--border);border-radius:16px;overflow:hidden;aspect-ratio:16/9}
.player-wrap iframe{width:100%;height:100%;border:0;display:block}
.lesson-meta{margin-top:18px}
.lesson-meta h2{margin-bottom:8px}
.lesson-list{background:var(--surface);border:1px solid var(--border);border-radius:16px;overflow:hidden;max-height:70vh;overflow-y:auto}
.lesson-list h3{font-size:13px;letter-spacing:.06em;text-transform:uppercase;color:var(--caption);padding:16px 18px;border-bottom:1px solid var(--border);position:sticky;top:0;background:var(--surface)}
.lesson-item{display:flex;gap:12px;align-items:flex-start;width:100%;text-align:left;padding:14px 18px;border-bottom:1px solid rgba(198,255,230,.06);transition:background-color .15s}
.lesson-item:last-child{border-bottom:none}
.lesson-item:hover{background:var(--surface-2)}
.lesson-item.active{background:var(--surface-2)}
.lesson-item.active .n{background:var(--mint);color:var(--cta-text);border-color:var(--mint)}
.lesson-item .n{flex:none;width:28px;height:28px;border-radius:8px;background:var(--bg-deep);border:1px solid var(--border);color:var(--mint);font-size:12px;font-weight:700;display:flex;align-items:center;justify-content:center}
.lesson-item .t{font-size:14px;line-height:20px;font-weight:500;color:var(--heading)}
.lesson-item .d{font-size:12px;color:var(--caption);margin-top:2px}

/* Trạng thái rỗng */
.empty{text-align:center;padding:60px 20px;max-width:520px;margin:0 auto}
.empty .ic{width:40px;height:40px;color:var(--border-strong);margin:0 auto 16px}
.empty h2{margin-bottom:10px}
.empty p{color:var(--muted);margin-bottom:22px}

footer.site{background:var(--bg-deep);border-top:1px solid var(--border);padding:36px 0;margin-top:40px}
footer.site .container{display:flex;flex-wrap:wrap;gap:12px 24px;justify-content:space-between;align-items:center}
footer.site p,footer.site a{font-size:13px;color:var(--caption);text-decoration:none}
footer.site a:hover{color:var(--mint)}