:root{
  --bg:#f7f8fb; --surface:#ffffff; --surface-2:#f1f3f9;
  --text:#171923; --text-muted:#6b7280; --border:#e5e7eb;
  --primary:#5b3df5; --primary-dark:#4429d1; --accent:#00c896;
  --warn:#f5a524; --danger:#f13154;
  --radius:14px; --shadow:0 2px 10px rgba(20,20,43,.06);
  --font:'Inter',system-ui,-apple-system,'Segoe UI',sans-serif;
}
[data-theme="dark"]{
  --bg:#0f1117; --surface:#171a23; --surface-2:#1e222c;
  --text:#f2f3f7; --text-muted:#98a0b3; --border:#2a2f3c;
  --shadow:0 2px 14px rgba(0,0,0,.4);
}
*{box-sizing:border-box}
body{margin:0;font-family:var(--font);background:var(--bg);color:var(--text);line-height:1.5}
a{color:inherit;text-decoration:none}
.container{max-width:1080px;margin:0 auto;padding:0 20px}
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;padding:12px 22px;border-radius:10px;border:none;font-weight:600;font-size:15px;cursor:pointer;transition:.15s}
.btn-primary{background:var(--primary);color:#fff}
.btn-primary:hover{background:var(--primary-dark)}
.btn-outline{background:transparent;border:1.5px solid var(--border);color:var(--text)}
.btn-outline:hover{border-color:var(--primary);color:var(--primary)}
.btn-accent{background:var(--accent);color:#00291f}
.btn-sm{padding:8px 14px;font-size:13px;border-radius:8px}
.btn:disabled{opacity:.5;cursor:not-allowed}

.navbar{position:sticky;top:0;z-index:50;background:var(--surface);border-bottom:1px solid var(--border)}
.navbar .container{display:flex;align-items:center;justify-content:space-between;height:64px}
.brand{font-weight:800;font-size:19px;display:flex;align-items:center;gap:8px}
.brand span.dot{width:9px;height:9px;border-radius:50%;background:var(--accent)}
.nav-links{display:flex;gap:22px;align-items:center}
.nav-links a{color:var(--text-muted);font-weight:600;font-size:14px}
.nav-links a.active,.nav-links a:hover{color:var(--primary)}

.hero{padding:76px 0 60px;text-align:center}
.hero h1{font-size:44px;line-height:1.15;margin:0 0 14px;font-weight:800}
.hero p{color:var(--text-muted);font-size:18px;margin:0 auto 30px;max-width:560px}
.hero-actions{display:flex;gap:14px;justify-content:center;flex-wrap:wrap}

.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);padding:20px}
.grid{display:grid;gap:16px}
.grid-2{grid-template-columns:repeat(2,1fr)}
.grid-3{grid-template-columns:repeat(3,1fr)}
.grid-4{grid-template-columns:repeat(4,1fr)}
@media(max-width:800px){.grid-2,.grid-3,.grid-4{grid-template-columns:1fr 1fr}}
@media(max-width:520px){.grid-2,.grid-3,.grid-4{grid-template-columns:1fr}}

.stat{padding:18px}
.stat .num{font-size:26px;font-weight:800}
.stat .label{color:var(--text-muted);font-size:13px;margin-top:2px}

.progress{height:10px;background:var(--surface-2);border-radius:99px;overflow:hidden}
.progress > div{height:100%;background:linear-gradient(90deg,var(--primary),var(--accent));border-radius:99px;transition:width .5s ease}

.badge-pill{display:inline-flex;align-items:center;gap:6px;background:var(--surface-2);border-radius:99px;padding:5px 12px;font-size:12px;font-weight:700}
.tag{display:inline-block;padding:3px 10px;border-radius:99px;font-size:11px;font-weight:700;background:var(--surface-2);color:var(--text-muted)}
.tag-easy{background:#e6f9f0;color:#0a8f52}
.tag-medium{background:#fff4e0;color:#b9740b}
.tag-hard{background:#ffe6e9;color:#c81e3a}
.tag-expert{background:#efe6ff;color:#6423d6}
[data-theme="dark"] .tag-easy{background:#0b3324;color:#3fd995}
[data-theme="dark"] .tag-medium{background:#3a2a08;color:#ffc267}
[data-theme="dark"] .tag-hard{background:#3a0a14;color:#ff7c93}
[data-theme="dark"] .tag-expert{background:#241249;color:#c3a3ff}

.task-row{display:flex;align-items:center;justify-content:space-between;gap:14px;padding:16px;border:1px solid var(--border);border-radius:12px;margin-bottom:10px;background:var(--surface)}
.task-row.done{opacity:.6}
.task-title{font-weight:700;margin-bottom:4px}
.task-meta{display:flex;gap:8px;align-items:center;color:var(--text-muted);font-size:13px}

.section-title{font-size:22px;font-weight:800;margin:36px 0 16px}
.form-group{margin-bottom:16px}
.form-group label{display:block;font-weight:600;font-size:13px;margin-bottom:6px}
.form-control{width:100%;padding:11px 14px;border-radius:10px;border:1.5px solid var(--border);background:var(--surface);color:var(--text);font-size:14px}
.form-control:focus{outline:none;border-color:var(--primary)}
.auth-card{max-width:420px;margin:60px auto;padding:32px}
.alert{padding:12px 16px;border-radius:10px;font-size:14px;margin-bottom:16px}
.alert-error{background:#ffe6e9;color:#c81e3a}
.alert-success{background:#e6f9f0;color:#0a8f52}

.footer{border-top:1px solid var(--border);padding:30px 0;color:var(--text-muted);font-size:13px;text-align:center;margin-top:60px}

/* toast for XP / level-up / badge animations */
.toast{position:fixed;bottom:24px;right:24px;background:var(--surface);border:1px solid var(--border);box-shadow:var(--shadow);border-radius:14px;padding:16px 20px;min-width:240px;z-index:200;animation:toast-in .25s ease}
.toast .xp-gain{color:var(--accent);font-weight:800;font-size:20px}
@keyframes toast-in{from{transform:translateY(20px);opacity:0}to{transform:translateY(0);opacity:1}}

.mobile-nav{display:none}
@media(max-width:720px){
  .nav-links{display:none}
  .mobile-nav{display:flex;position:fixed;bottom:0;left:0;right:0;background:var(--surface);border-top:1px solid var(--border);justify-content:space-around;padding:8px 0;z-index:60}
  .mobile-nav a{display:flex;flex-direction:column;align-items:center;font-size:11px;color:var(--text-muted);gap:2px}
  .mobile-nav a.active{color:var(--primary)}
  body{padding-bottom:64px}
  .hero h1{font-size:32px}
}