:root {
  --bg: #f5f5f7;
  --card-bg: #ffffff;
  --text: #1d1d1f;
  --text-secondary: #6e6e73;
  --text-tertiary: #86868b;
  --accent: #0071e3;
  --accent-hover: #0077ed;
  --accent-active: #006edb;
  --border: #d2d2d7;
  --field-bg: #f5f5f7;
  --danger: #e30000;
  --danger-bg: #fff0f0;
  --radius-card: 18px;
  --radius-field: 12px;
  --shadow: 0 12px 40px rgba(0, 0, 0, 0.08), 0 1px 2px rgba(0, 0, 0, 0.04);
}

* { box-sizing: border-box; margin: 0; padding: 0; }

html, body { height: 100%; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "SF Pro Display",
    "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 32px 20px;
}

.auth-wrap {
  width: 100%;
  max-width: 400px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 24px;
}

.card {
  width: 100%;
  background: var(--card-bg);
  border-radius: var(--radius-card);
  box-shadow: var(--shadow);
  padding: 40px 36px 36px;
  display: flex;
  flex-direction: column;
  align-items: stretch;
}

.card.center { text-align: center; align-items: center; }

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 28px;
}

.card.center .brand { justify-content: center; }

.brand-mark {
  width: 34px;
  height: 34px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
}

.brand-name {
  font-size: 17px;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.title {
  font-size: 26px;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: 6px;
}

.subtitle {
  font-size: 15px;
  color: var(--text-secondary);
  line-height: 1.45;
  margin-bottom: 26px;
}

.subtitle strong { color: var(--text); font-weight: 600; }

/* Tab 切换 */
.tabs {
  position: relative;
  display: grid;
  grid-template-columns: 1fr 1fr;
  background: var(--field-bg);
  border-radius: 10px;
  padding: 3px;
  margin-bottom: 24px;
}

.tab {
  position: relative;
  z-index: 1;
  border: none;
  background: transparent;
  font: inherit;
  font-size: 14px;
  font-weight: 500;
  color: var(--text-secondary);
  padding: 9px 0;
  border-radius: 8px;
  cursor: pointer;
  transition: color 0.2s ease;
}

.tab.is-active { color: var(--text); }

.tab-glider {
  position: absolute;
  top: 3px;
  bottom: 3px;
  left: 3px;
  width: calc(50% - 3px);
  background: #fff;
  border-radius: 8px;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.12);
  transition: transform 0.24s cubic-bezier(0.4, 0, 0.2, 1);
}

.tabs[data-mode="signup"] .tab-glider { transform: translateX(100%); }

/* 表单面板 */
.panel {
  display: none;
  flex-direction: column;
  gap: 16px;
}

.panel.is-visible { display: flex; }

.field { display: flex; flex-direction: column; gap: 6px; }

.field-label {
  font-size: 13px;
  font-weight: 500;
  color: var(--text-secondary);
}

.input {
  font: inherit;
  font-size: 16px;
  color: var(--text);
  background: var(--field-bg);
  border: 1px solid transparent;
  border-radius: var(--radius-field);
  padding: 12px 14px;
  outline: none;
  transition: border-color 0.18s ease, background 0.18s ease, box-shadow 0.18s ease;
  width: 100%;
}

.input::placeholder { color: var(--text-tertiary); }

.input:focus {
  background: #fff;
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(0, 113, 227, 0.15);
}

.btn {
  font: inherit;
  font-size: 16px;
  font-weight: 500;
  color: #fff;
  background: var(--accent);
  border: none;
  border-radius: var(--radius-field);
  padding: 13px 0;
  margin-top: 6px;
  cursor: pointer;
  width: 100%;
  transition: background 0.18s ease, transform 0.05s ease;
}

.btn:hover { background: var(--accent-hover); }
.btn:active { background: var(--accent-active); transform: scale(0.99); }

.btn-secondary {
  color: var(--accent);
  background: transparent;
  border: 1px solid var(--accent);
  text-decoration: none;
  text-align: center;
}

.btn-secondary:hover { background: rgba(0, 113, 227, 0.06); }

.switch-hint {
  font-size: 13px;
  color: var(--text-secondary);
  text-align: center;
  margin-top: 2px;
}

.switch-hint a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 500;
}

.switch-hint a:hover { text-decoration: underline; }

/* 错误提示 */
.alert {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  background: var(--danger-bg);
  color: var(--danger);
  font-size: 13px;
  line-height: 1.45;
  padding: 11px 13px;
  border-radius: 10px;
  margin-bottom: 20px;
}

.alert svg { flex-shrink: 0; margin-top: 1px; }

.info-box {
  background: var(--field-bg);
  border-radius: 12px;
  padding: 16px 18px;
  font-size: 13px;
  color: var(--text-secondary);
  line-height: 1.6;
  text-align: left;
  margin: 4px 0 20px;
}

.info-box p + p { margin-top: 8px; }

/* 页脚 */
.foot {
  text-align: center;
  font-size: 13px;
  color: var(--text-secondary);
  line-height: 1.6;
}

.foot-muted { color: var(--text-tertiary); font-size: 12px; }

@media (max-width: 420px) {
  .card { padding: 32px 24px 28px; }
}