:root { --fg:#111; --muted:#6b7280; --bg:#fff; --line:#e5e7eb; --primary:#2563eb; }
*{box-sizing:border-box} html,body{margin:0;padding:0}
body{font-family:system-ui,-apple-system,Segoe UI,Roboto,Helvetica,Arial,sans-serif;color:var(--fg);background:var(--bg);line-height:1.6}
a{color:var(--primary);text-decoration:none}
a:hover{text-decoration:underline}

.container{max-width:960px;margin:0 auto;padding:0 16px}
.row{display:flex;gap:12px}
.between{justify-content:space-between}
.center{align-items:center}

.site-header{border-bottom:1px solid var(--line);position:sticky;top:0;background:#fff;z-index:10}
.brand{font-weight:700;font-size:20px}
.nav{display:none;gap:12px}
.nav a{padding:8px 10px;border-radius:10px}
.nav a.btn{background:var(--primary);color:#fff}
.nav-toggle{border:1px solid var(--line);background:#fff;border-radius:8px;padding:6px 10px}

.site-footer{border-top:1px solid var(--line);margin-top:40px;padding:20px 0;color:var(--muted)}

.card{border:1px solid var(--line);border-radius:12px;padding:16px;margin:12px 0}
.grid{display:grid;gap:16px}
.grid-2{grid-template-columns:1fr}
label{display:block;margin:8px 0 4px}
input[type="text"],input[type="email"],input[type="password"]{width:100%;padding:10px;border:1px solid var(--line);border-radius:10px}
button, .btn-primary{background:var(--primary);color:#fff;border:none;padding:10px 14px;border-radius:10px;cursor:pointer}
button:hover, .btn-primary:hover{opacity:.9}

/* モバイル: デフォルトが縦並び */
.nav-open .nav{display:flex;flex-direction:column;position:absolute;right:16px;top:56px;background:#fff;border:1px solid var(--line);padding:8px;border-radius:12px}

/* タブレット以上 */
@media (min-width: 768px){
  .nav{display:flex}
  .nav-toggle{display:none}
  .grid-2{grid-template-columns:1fr 1fr}
}