:root{
  --bg1:#0b2a22; --bg2:#0f3a2d;
  --panel:#113f31; --panel2:#0f3329;
  --text:#eafff6; --muted:#c8efe1;
  --brand:#34d399; --brand-dk:#059669;
  --good:#22c55e; --bad:#ef4444;
  --border:#1a5a49; --radius:16px;
  --shadow:0 14px 38px rgba(0,0,0,.35);
  --maxw:1200px; --gap:16px;
  --transition:.22s cubic-bezier(.22,.61,.36,1);
}

*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family:system-ui,-apple-system,Segoe UI,Roboto,"Helvetica Neue",Arial,"Noto Sans",sans-serif;
  color:var(--text);
  background:
    radial-gradient(1200px 600px at 50% -120px, rgba(52,211,153,.18) 0%, transparent 60%),
    linear-gradient(180deg,var(--bg2),var(--bg1));
}

.page{min-height:100dvh;display:flex;flex-direction:column}
.container-inner{width:min(100% - 32px,var(--maxw));margin-inline:auto}

/* Header / Menu */
.site-header{
  position:sticky;top:0;z-index:20;
  background:rgba(9,39,30,.85);
  backdrop-filter:blur(8px);
  border-bottom:1px solid var(--border);
  box-shadow:0 8px 22px rgba(0,0,0,.25);
}
.site-header .container-inner{
  display:flex;align-items:center;justify-content:space-between;padding:12px 0
}
.brand{color:var(--text);text-decoration:none;font-weight:800;font-size:1.1rem;letter-spacing:.3px}
.nav{display:flex;gap:8px;align-items:center}
.nav-link{
  text-decoration:none;color:var(--muted);padding:8px 12px;border-radius:999px;border:1px solid transparent;transition:var(--transition)
}
.nav-link:hover,.nav-link.active{
  color:var(--text);border-color:var(--border);background:rgba(5,150,105,.18);
  box-shadow:0 6px 16px rgba(5,150,105,.22)
}

/* Ad slots */
.ad-slot{
  display:flex;align-items:center;justify-content:center;min-height:90px;margin:12px auto 0;
  border:1px dashed rgba(255,255,255,.18);border-radius:var(--radius);background:#0c2f25;color:var(--muted);
  text-align:center;padding:8px
}
.ad-bottom{margin:18px auto}
@media (max-width:600px){.ad-slot{min-height:50px}}

.site-main{flex:1 1 auto;display:block;padding:18px 0 22px}

/* Toolbar */
.toolbar{display:grid;gap:var(--gap);grid-template-columns:1fr;margin-bottom:10px}
.page-title{margin:0;font-size:clamp(22px,2.6vw,34px);font-weight:900;letter-spacing:.2px}

.options{
  display:grid;gap:var(--gap);grid-template-columns:repeat(4,minmax(180px,1fr));
  background:var(--panel);border:1px solid var(--border);border-radius:var(--radius);padding:14px;box-shadow:var(--shadow)
}
.option{display:grid;gap:8px;align-content:start}
.option label{font-size:13px;color:var(--muted)}
.option.buttons{align-items:end}
select,input[type="number"]{
  appearance:none;background:var(--panel2);color:var(--text);border:1px solid var(--border);border-radius:12px;padding:12px 14px;
  font-weight:700;outline:none;transition:var(--transition)
}
select:focus,input[type="number"]:focus{border-color:var(--brand);box-shadow:0 0 0 3px rgba(52,211,153,.25)}

.btn{
  background:linear-gradient(180deg,var(--brand),var(--brand-dk));color:#06271f;padding:12px 16px;font-weight:900;
  border:1px solid rgba(255,255,255,.12);border-radius:12px;cursor:pointer;transition:transform .08s ease, box-shadow var(--transition);
  box-shadow:0 10px 22px rgba(0,0,0,.25)
}
.btn:hover{transform:translateY(-1px)}
.btn:active{transform:translateY(0)}
.btn.ghost{
  background:#0f3329;color:var(--text)
}

/* Summary */
.summary{
  display:flex;gap:14px;align-items:center;flex-wrap:wrap;
  background:var(--panel);border:1px solid var(--border);border-radius:12px;padding:10px 12px;box-shadow:var(--shadow)
}
.sum-item{font-weight:800}
.sum-item.ok{color:var(--good)}
.sum-item.wrong{color:var(--bad)}

/* Questions grid */
.questions{
  margin-top:16px;display:grid;gap:var(--gap);
  grid-template-columns:repeat(auto-fit,minmax(260px,1fr))
}

/* Card */
.q-card{
  background:var(--panel);border:1px solid var(--border);border-radius:18px;padding:16px;box-shadow:var(--shadow);
  display:grid;gap:10px;position:relative
}
.q-head{display:flex;align-items:center;justify-content:space-between;gap:10px;font-weight:900;letter-spacing:.2px}
.q-op{font-size:14px;color:var(--muted)}
.q-body{
  font-size:clamp(26px,3vw,36px); /* TO, RÕ, DỄ NHÌN */
  font-weight:900;letter-spacing:.3px;line-height:1.25
}
.q-input{
  background:var(--panel2);color:var(--text);border:2px solid transparent;
  border-radius:12px;padding:12px 12px;font-weight:800;font-size:18px;outline:none;transition:var(--transition);width:100%
}
.q-input:focus{border-color:var(--brand);box-shadow:0 0 0 3px rgba(52,211,153,.25)}

/* Kết quả từng câu */
.q-result{
  position:absolute;right:12px;bottom:12px;font-size:22px;font-weight:900
}
.q-card.correct{outline:3px solid rgba(34,197,94,.7)}
.q-card.wrong{outline:3px solid rgba(239,68,68,.7)}
.q-result.ok{color:var(--good)}    /* ✓ */
.q-result.bad{color:var(--bad)}    /* ✗ */

/* Footer */
.site-footer{margin-top:6px;border-top:1px solid var(--border);background:#0a2a21}
.site-footer .container-inner{padding:16px 0 20px;text-align:center;color:var(--muted);font-size:14px}
.footer-link{color:var(--text);text-decoration:none}
.footer-link:hover{text-decoration:underline}

/* Responsive */
@media (max-width:900px){.options{grid-template-columns:repeat(2,minmax(160px,1fr))}}
@media (max-width:560px){.options{grid-template-columns:1fr}}