:root{
  --chu:#1c1d1f; --mo:#6a6f73; --vien:#d1d7dc; --nen:#f7f9fa; --trang:#fff;
  --chinh:#1f4e8c; --chinh-dam:#173b6b; --xanh:#1e7a46; --do:#b3261e; --vang:#9a6700;
  --bo:4px;
}
*{box-sizing:border-box}
html,body{margin:0}
body{font:15px/1.5 -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Helvetica Neue",Arial,sans-serif;
  color:var(--chu);background:var(--nen);-webkit-font-smoothing:antialiased}
button,input,select,textarea{font:inherit;color:inherit}
a{color:var(--chinh)}
[hidden]{display:none!important}

.dau{height:56px;background:var(--trang);border-bottom:1px solid var(--vien);display:flex;align-items:center;
  justify-content:space-between;padding:0 16px;position:sticky;top:0;z-index:20}
.hieu{display:flex;align-items:baseline;gap:8px;text-decoration:none;color:var(--chu)}
.hieu b{font-size:17px;letter-spacing:.5px}
.hieu span{color:var(--mo);font-size:15px}
.dau-phai{display:flex;align-items:center;gap:10px}
.ten-toi{background:none;border:1px solid var(--vien);border-radius:var(--bo);padding:6px 12px;cursor:pointer;
  max-width:200px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}

.nut{background:var(--chinh);color:#fff;border:0;border-radius:var(--bo);padding:9px 16px;font-weight:600;cursor:pointer}
.nut:hover{background:var(--chinh-dam)}
.nut:disabled{opacity:.55;cursor:default}
.nut-vien{background:var(--trang);color:var(--chu);border:1px solid var(--chu);border-radius:var(--bo);padding:8px 14px;
  font-weight:600;cursor:pointer;text-decoration:none;display:inline-block}
.nut-chu{background:none;border:0;color:var(--mo);cursor:pointer;padding:8px 10px}
.mo{color:var(--mo)}
.bao{color:var(--do);min-height:1.5em;margin:6px 0;font-size:14px}
.bao.tot{color:var(--xanh)}

/* Dang nhap */
.o-vao{max-width:380px;margin:9vh auto;background:var(--trang);border:1px solid var(--vien);border-radius:var(--bo);padding:28px}
.o-vao h1{font-size:22px;margin:0 0 4px}
.o-vao p{margin:0 0 18px}
label{display:block;font-weight:600;font-size:14px;margin:12px 0 0}
input[type=text],input[type=password],input[type=email],input[type=tel],select,textarea{display:block;width:100%;margin-top:6px;
  padding:10px 12px;border:1px solid var(--chu);border-radius:var(--bo);background:#fff;font-weight:400}
textarea{min-height:80px;resize:vertical}
.o-vao .nut{width:100%;margin-top:14px;padding:11px}

/* Trang khoa hoc cua toi */
.ruot{max-width:1120px;margin:0 auto;padding:28px 16px 60px}
.ruot h1{font-size:26px;margin:0 0 4px}
.luoi-khoa{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:20px;margin-top:22px}
.the-khoa{background:var(--trang);border:1px solid var(--vien);border-radius:var(--bo);overflow:hidden;cursor:pointer;
  display:flex;flex-direction:column;text-align:left;padding:0}
.the-khoa:hover{box-shadow:0 2px 8px rgba(0,0,0,.08)}
.the-khoa .bia{aspect-ratio:16/9;background:#2d2f31 center/cover no-repeat;display:flex;align-items:flex-end}
.the-khoa .than{padding:14px 16px 16px;flex:1;display:flex;flex-direction:column;gap:6px}
.the-khoa h3{margin:0;font-size:16px;line-height:1.35}
.the-khoa .mo{font-size:13px}
.thanh{height:4px;background:#e5e7ea;border-radius:2px;overflow:hidden;margin-top:auto}
.thanh i{display:block;height:100%;background:var(--chinh)}
.rong{background:var(--trang);border:1px dashed var(--vien);border-radius:var(--bo);padding:36px;text-align:center;margin-top:22px}

/* Man hoc */
.hoc{display:grid;grid-template-columns:minmax(0,1fr) 360px;min-height:calc(100vh - 56px)}
.hoc-trai{background:var(--trang);min-width:0}
.hoc-phai{background:var(--trang);border-left:1px solid var(--vien);max-height:calc(100vh - 56px);overflow:auto;position:sticky;top:56px}
.hoc-phai h2{font-size:16px;margin:0;padding:16px;border-bottom:1px solid var(--vien)}
.chu-de{border-bottom:1px solid var(--vien)}
.chu-de>button{width:100%;text-align:left;background:var(--nen);border:0;padding:14px 16px;cursor:pointer;
  display:flex;justify-content:space-between;gap:10px}
.chu-de>button b{font-size:15px}
.chu-de>button span{color:var(--mo);font-size:13px;white-space:nowrap}
.dong-bai{display:flex;gap:12px;padding:10px 16px;cursor:pointer;border:0;background:none;width:100%;text-align:left;align-items:flex-start}
.dong-bai:hover{background:#eef1f4}
.dong-bai.dang{background:#e3e9f2}
.dong-bai .dau-tick{width:18px;height:18px;border:1.5px solid var(--chu);border-radius:3px;flex:none;margin-top:2px;
  display:flex;align-items:center;justify-content:center;font-size:12px;color:#fff}
.dong-bai.xong .dau-tick{background:var(--chu)}
.dong-bai .ten-bai{font-size:14px}
.dong-bai .gio{font-size:12px;color:var(--mo);display:block;margin-top:2px}

.khung-video{position:relative;background:#000;aspect-ratio:16/9;width:100%;overflow:hidden;user-select:none;-webkit-user-select:none;
  -webkit-touch-callout:none}
.khung-video video{position:absolute;inset:0;width:100%;height:100%;background:#000;pointer-events:none}
.khung-video.to{position:fixed;inset:0;z-index:100;aspect-ratio:auto;height:100%}
.chim{position:absolute;z-index:3;pointer-events:none;color:rgba(255,255,255,.55);font-size:clamp(11px,1.6vw,16px);font-weight:600;
  text-shadow:0 0 3px rgba(0,0,0,.7);white-space:nowrap;transition:none}
.chim-lat{position:absolute;inset:-50%;z-index:2;pointer-events:none;display:flex;flex-wrap:wrap;align-content:space-around;
  justify-content:space-around;transform:rotate(-24deg);opacity:.09;color:#fff;font-size:15px;font-weight:600;gap:60px 90px;overflow:hidden}
.man-che{position:absolute;inset:0;z-index:7;overflow:auto;background:rgba(0,0,0,.86);color:#fff;display:flex;flex-direction:column;
  align-items:center;justify-content:center;gap:14px;text-align:center;padding:20px}
.man-che p{margin:0;max-width:440px}
.bam-phat{position:absolute;inset:0;z-index:4}
.dieu-khien{position:absolute;left:0;right:0;bottom:0;z-index:6;padding:26px 12px 8px;
  background:linear-gradient(transparent,rgba(0,0,0,.75));color:#fff;opacity:0;transition:opacity .2s}
.khung-video:hover .dieu-khien,.khung-video.dung .dieu-khien,.khung-video.cham .dieu-khien{opacity:1}
.thanh-tua{width:100%;accent-color:#fff;margin:0 0 6px;height:4px;cursor:pointer}
.hang-dk{display:flex;align-items:center;gap:6px}
.hang-dk button{background:none;border:0;color:#fff;cursor:pointer;padding:6px 8px;border-radius:3px;font-size:14px;min-width:34px}
.hang-dk button:hover{background:rgba(255,255,255,.15)}
.hang-dk .gio-dk{font-size:13px;font-variant-numeric:tabular-nums;margin-right:auto;padding-left:4px}
.hang-dk select{background:rgba(0,0,0,.4);color:#fff;border:1px solid rgba(255,255,255,.35);border-radius:3px;padding:3px 4px;font-size:13px;width:auto;margin:0;display:inline-block}
.dang-tai{position:absolute;z-index:4;left:50%;top:50%;width:42px;height:42px;margin:-21px;border:3px solid rgba(255,255,255,.25);
  border-top-color:#fff;border-radius:50%;animation:xoay 0.9s linear infinite}
@keyframes xoay{to{transform:rotate(360deg)}}
.duoi-video{padding:18px 24px 40px;max-width:900px}
.duoi-video h1{font-size:22px;margin:0 0 4px}
.duoi-video .mo-ta{white-space:pre-wrap;margin-top:14px}
.hang-nut{display:flex;gap:10px;flex-wrap:wrap;align-items:center;margin-top:16px}
.nhac-nho{font-size:13px;color:var(--mo);margin-top:18px;border-top:1px solid var(--vien);padding-top:12px}

.hop-nen{position:fixed;inset:0;background:rgba(0,0,0,.45);z-index:200;display:flex;align-items:center;justify-content:center;padding:16px}
.hop{background:#fff;border-radius:var(--bo);padding:22px;width:100%;max-width:420px;max-height:90vh;overflow:auto}
.hop h3{margin:0 0 6px;font-size:18px}

.dong-bai.bi-khoa{opacity:.55;cursor:not-allowed}
.dong-bai.bi-khoa .dau-tick{border-color:transparent;font-size:13px}
.khoi-kiem{padding:16px;border-bottom:1px solid var(--vien);background:#fbfbf8}
.hop-kiem{max-width:680px}
.cau{border:1px solid var(--vien);border-radius:var(--bo);margin:12px 0;padding:10px 14px}
.cau legend{padding:0 4px}
.cau.sai{border-color:var(--do);background:#fdf3f2}
.cau.dung{border-color:#9ccfb0}
.lua{display:flex;gap:8px;align-items:flex-start;font-weight:400;margin:8px 0 0;cursor:pointer}
.lua input{margin-top:4px}
.ket{font-weight:700}
.ket.dat{color:var(--xanh)}
.ket.truot{color:var(--do)}
@media (max-width:900px){
  .hoc{grid-template-columns:1fr}
  .hoc-phai{position:static;max-height:none;border-left:0;border-top:1px solid var(--vien)}
  .duoi-video{padding:14px 16px 20px}
  .duoi-video h1{font-size:18px}
  .dieu-khien{opacity:1}
  .hang-dk .an-dt{display:none}
  .man-che{gap:8px;padding:10px 14px;font-size:14px;line-height:1.4}
  .man-che .nut{padding:7px 14px}
}
@media print{body{display:none!important}}