:root{--red:#b91c1c;--red2:#7f1d1d;--gold:#f5b301;--dark:#171717;--cream:#fffaf0;--line:#eadfce;--muted:#667085;--green:#16803b;--blue:#2563eb}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;font-family:Arial,"Noto Sans SC",sans-serif;background:#f6f7f9;color:#222;line-height:1.6}
button,select,input{font:inherit}
a{color:inherit;text-decoration:none}
.container{width:min(1180px,92%);margin:auto}
.header{position:sticky;top:0;z-index:30;background:#fff;border-bottom:1px solid #eee}
.header-inner{height:74px;display:flex;align-items:center;gap:24px}
.logo{display:flex;align-items:center;gap:10px;font-weight:900}
.logo img{width:54px;height:54px;object-fit:contain}
.logo span{color:var(--red);font-size:20px}
nav{margin-left:auto;display:flex;gap:20px;font-weight:700}
nav a:hover,.active{color:var(--red)}
.hero{background:linear-gradient(135deg,#161616,#4d0a0a 60%,#7f1d1d);color:#fff;padding:68px 0 78px}
.hero-grid{display:grid;grid-template-columns:1.25fr .75fr;gap:36px;align-items:center}
.badge{display:inline-block;background:var(--gold);color:#111;padding:7px 13px;border-radius:999px;font-weight:900}
h1{font-size:clamp(36px,5vw,62px);line-height:1.08;margin:18px 0}
h1 span{color:#ffd24c}
.hero p{font-size:18px;color:#f4e8e8;max-width:700px}
.hero-board{background:#fff;color:#222;border-radius:24px;padding:26px;box-shadow:0 24px 70px #0006}
.hero-word{font-size:70px;font-weight:900;text-align:center;color:var(--red);line-height:1.15}
.hero-board .py{text-align:center;color:var(--red);font-weight:800;font-size:20px}
.hero-board .vi{text-align:center;font-weight:700}
.hero-note{margin-top:18px;padding:13px;border-radius:12px;background:#fff7e2;border:1px solid #f2d48a}
.stats{margin-top:-30px;position:relative;z-index:2}
.stats-grid{display:grid;grid-template-columns:repeat(4,1fr);background:#fff;border-radius:18px;box-shadow:0 12px 35px #0001;overflow:hidden}
.stat{padding:22px;text-align:center;border-right:1px solid #eee}
.stat:last-child{border:0}
.stat b{display:block;font-size:28px;color:var(--red)}
.main{padding:42px 0 76px}
.toolbar{background:#fff;border:1px solid #eee;border-radius:22px;padding:22px;box-shadow:0 12px 30px #0000000a}
.controls{display:grid;grid-template-columns:1.2fr repeat(3,.7fr);gap:12px}
.control{width:100%;padding:12px 14px;border:1px solid #ddd;border-radius:12px;background:#fff}
.mode-row{display:flex;flex-wrap:wrap;gap:10px;margin-top:14px}
.chip{border:1px solid #ddd;background:#fff;padding:9px 13px;border-radius:999px;cursor:pointer;font-weight:800}
.chip.active{background:var(--red);border-color:var(--red);color:#fff}
.progress-panel{margin-top:18px;display:grid;grid-template-columns:1fr auto;gap:16px;align-items:center}
.progress-track{height:12px;background:#eee;border-radius:999px;overflow:hidden}
.progress-bar{height:100%;width:0;background:linear-gradient(90deg,var(--gold),var(--green));transition:.3s}
.progress-text{font-weight:900;color:var(--red)}
.study-layout{display:grid;grid-template-columns:1fr 310px;gap:24px;margin-top:24px}
.card-zone{min-width:0}
.flash-stage{perspective:1200px;min-height:520px}
.flashcard{position:relative;width:100%;min-height:520px;transform-style:preserve-3d;transition:transform .55s;cursor:pointer}
.flashcard.flip{transform:rotateY(180deg)}
.face{position:absolute;inset:0;backface-visibility:hidden;border-radius:28px;border:1px solid #eadfce;background:#fff;box-shadow:0 22px 55px #00000012;overflow:hidden}
.back{transform:rotateY(180deg)}
.card-top{display:flex;justify-content:space-between;align-items:center;padding:18px 22px;border-bottom:1px solid #eee;background:linear-gradient(90deg,#fff9ed,#fff)}
.lesson-tag{font-weight:900;color:var(--red)}
.status-tag{padding:6px 10px;border-radius:999px;background:#f3f4f6;font-size:13px;font-weight:800}
.card-main{min-height:390px;display:grid;place-items:center;text-align:center;padding:34px}
.hanzi{font-size:clamp(72px,12vw,130px);font-weight:900;line-height:1;color:#171717}
.pinyin{font-size:28px;color:var(--red);font-weight:900;margin-top:18px}
.hint{color:var(--muted);margin-top:24px}
.back-content{padding:30px}
.meaning{font-size:36px;font-weight:900;color:var(--red);margin-bottom:4px}
.type{font-weight:800;color:#555}
.example{margin-top:22px;padding:18px;border-radius:16px;background:#fff8e8;border:1px solid #f1dfb1}
.example-cn{font-size:25px;font-weight:900}
.example-py{color:var(--red);font-weight:800;margin:5px 0}
.example-vi{color:#444}
.memory-tip{margin-top:18px;padding:16px;border-left:5px solid var(--gold);background:#fffdf5;border-radius:12px}
.card-footer{display:flex;justify-content:center;gap:10px;padding:18px;border-top:1px solid #eee;flex-wrap:wrap}
.btn{border:0;border-radius:12px;padding:12px 16px;font-weight:900;cursor:pointer;transition:.2s}
.btn:hover{transform:translateY(-2px)}
.btn-light{background:#fff;border:1px solid #ddd}
.btn-red{background:var(--red);color:#fff}
.btn-blue{background:var(--blue);color:#fff}
.btn-green{background:var(--green);color:#fff}
.side{display:grid;gap:16px;align-content:start}
.panel{background:#fff;border:1px solid #eee;border-radius:18px;padding:18px}
.panel h3{margin:0 0 12px}
.mini-stats{display:grid;grid-template-columns:repeat(3,1fr);gap:8px}
.mini{padding:12px 6px;border-radius:12px;background:#f7f8fa;text-align:center}
.mini b{display:block;font-size:21px;color:var(--red)}
.lesson-list{max-height:300px;overflow:auto;display:grid;gap:7px}
.lesson-btn{text-align:left;border:0;background:#f7f7f7;padding:10px;border-radius:10px;cursor:pointer}
.lesson-btn.active{background:var(--red);color:#fff}
.study-tips{margin:0;padding-left:20px}
.study-tips li{margin:7px 0}
.empty{display:none;background:#fff;border:1px dashed #ccc;border-radius:18px;padding:40px;text-align:center}
.keyboard{font-size:13px;color:#666;margin-top:12px;text-align:center}
kbd{background:#fff;border:1px solid #ccc;border-bottom-width:2px;border-radius:5px;padding:2px 6px}
.footer{background:#171717;color:#ddd;padding:38px 0;text-align:center}
@media(max-width:900px){
 .hero-grid,.study-layout{grid-template-columns:1fr}
 .stats-grid{grid-template-columns:repeat(2,1fr)}
 .controls{grid-template-columns:1fr 1fr}
 nav{display:none}
 .side{grid-template-columns:1fr 1fr}
}
@media(max-width:600px){
 .controls{grid-template-columns:1fr}
 .side{grid-template-columns:1fr}
 .flash-stage,.flashcard{min-height:550px}
 .hanzi{font-size:78px}
 .card-main{padding:22px}
 .back-content{padding:20px}
 .stats-grid{grid-template-columns:1fr 1fr}
 .stat{padding:16px}
 .hero{padding-top:48px}
}