:root {
  --ink: #1a1a1a;
  --muted: #6b7280;
  --line: #e5e7eb;
  --accent: #111827;
  --bg: #f6f7f9;
  --err: #b91c1c;
}
* { box-sizing: border-box; }
body {
  margin: 0; min-height: 100vh; display: grid; place-items: center;
  background: var(--bg); color: var(--ink);
  font: 15px/1.55 -apple-system, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  padding: 24px;
}
.card {
  width: 100%; max-width: 360px; background: #fff; border: 1px solid var(--line);
  border-radius: 14px; padding: 28px 26px; box-shadow: 0 1px 2px rgba(0,0,0,.04);
}
.brand { display: flex; align-items: center; justify-content: space-between; }
.logo { font-weight: 700; letter-spacing: .2px; color: var(--ink); text-decoration: none; }
.lang a { color: var(--muted); text-decoration: none; font-size: 13px; margin-left: 8px; }
.lang a.on { color: var(--ink); font-weight: 600; }
.tagline { color: var(--muted); font-size: 13px; margin: 6px 0 18px; }
h1 { font-size: 20px; margin: 0 0 16px; }
label { display: block; font-size: 13px; color: var(--muted); margin-bottom: 12px; }
input[type=email], input[type=password], input[type=text] {
  display: block; width: 100%; margin-top: 5px; padding: 10px 11px;
  border: 1px solid var(--line); border-radius: 9px; font-size: 15px; color: var(--ink);
}
input:focus { outline: none; border-color: var(--accent); }
button {
  width: 100%; margin-top: 6px; padding: 11px; border: 0; border-radius: 9px;
  background: var(--accent); color: #fff; font-size: 15px; font-weight: 600; cursor: pointer;
}
button.ghost { background: #fff; color: var(--ink); border: 1px solid var(--line); }
button:hover { opacity: .92; }
.alt { margin: 16px 0 0; text-align: center; font-size: 13px; }
.alt a { color: var(--accent); }
.who { margin: 0 0 16px; }
.error {
  background: #fef2f2; color: var(--err); border: 1px solid #fecaca;
  border-radius: 9px; padding: 9px 11px; font-size: 13px; margin: 0 0 14px;
}
.oauth { margin-top: 18px; }
.sep {
  display: flex; align-items: center; gap: 10px; color: var(--muted);
  font-size: 12px; margin: 2px 0 14px;
}
.sep::before, .sep::after {
  content: ""; flex: 1; height: 1px; background: var(--line);
}
.oauth-btn {
  display: block; width: 100%; margin-top: 8px; padding: 11px;
  border: 1px solid var(--line); border-radius: 9px; background: #fff;
  color: var(--ink); font-size: 15px; font-weight: 600; text-align: center;
  text-decoration: none;
}
.oauth-btn:hover { background: var(--bg); }
.oauth-github { border-color: #d0d7de; }
.oauth-google { border-color: #dadce0; }