:root {
  --color-primary: #7455B0;
  --color-primary-hover: #8A68C9;
  --color-bg: #F8F5FC;
  --color-surface: #FFFFFF;
  --color-surface-soft: #F3ECFB;
  --color-border: #E6DDF3;
  --color-text: #2F2F35;
  --color-muted: #6B7280;
  --color-info: #4F7FD9;
  --color-success: #22A06B;
  --color-warning: #F59E0B;
  --color-danger: #E5484D;
  --color-disabled: #E5E7EB;
  --shadow-card: 0 8px 24px rgba(116, 85, 176, 0.12);
  --shadow-card-hover: 0 12px 28px rgba(116, 85, 176, 0.18);
  --shadow-soft: 0 4px 14px rgba(47, 47, 53, 0.08);
  --radius-card: 8px;
  --radius-button: 8px;
  --radius-control: 8px;
  --page-width: 1120px;
  --content-width: 960px;
}

* {
  box-sizing: border-box;
}

html {
  min-width: 0;
}

body.math-app {
  margin: 0;
  min-height: 100vh;
  overflow-x: hidden;
  background:
    radial-gradient(circle at 10% 12%, rgba(116, 85, 176, 0.08), transparent 24%),
    radial-gradient(circle at 86% 18%, rgba(79, 127, 217, 0.08), transparent 22%),
    var(--color-bg);
  color: var(--color-text);
  font-family: "Noto Sans SC", "Microsoft YaHei", Arial, sans-serif;
  line-height: 1.6;
}

a {
  color: inherit;
}

.app-page {
  width: min(100% - 32px, var(--page-width));
  margin: 0 auto;
  padding: 40px 0;
}

.lesson-page {
  width: min(100% - 32px, var(--content-width));
  margin: 0 auto;
  padding: 22px 0 42px;
}

.site-topbar {
  display: grid;
  grid-template-columns: minmax(120px, 1fr) auto minmax(120px, 1fr);
  align-items: center;
  gap: 16px;
  min-height: 64px;
  margin-bottom: 28px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--color-border);
}

.site-topbar h1 {
  margin: 0;
  color: var(--color-primary);
  font-size: 28px;
  line-height: 1.25;
  text-align: center;
}

.site-topbar .tag {
  justify-self: end;
}

.site-topbar .btn {
  min-height: 36px;
  justify-self: start;
  padding: 7px 12px;
  font-size: 14px;
  box-shadow: none;
}

.btn,
button.btn,
a.btn {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border: 1px solid transparent;
  border-radius: var(--radius-button);
  padding: 10px 16px;
  font: inherit;
  font-size: 15px;
  font-weight: 700;
  line-height: 1.2;
  text-align: center;
  text-decoration: none;
  cursor: pointer;
  transition: background-color 0.18s ease, border-color 0.18s ease, color 0.18s ease, transform 0.18s ease, box-shadow 0.18s ease;
}

.btn-primary {
  background: var(--color-primary);
  color: #fff;
  box-shadow: 0 6px 14px rgba(116, 85, 176, 0.22);
}

.btn-primary:hover {
  background: var(--color-primary-hover);
  transform: translateY(-1px);
}

.btn-secondary {
  background: #fff;
  color: var(--color-text);
  border-color: var(--color-border);
}

.btn-secondary:hover {
  color: var(--color-primary);
  border-color: var(--color-primary);
}

.btn-disabled,
.btn:disabled {
  background: var(--color-disabled);
  color: var(--color-muted);
  border-color: var(--color-disabled);
  box-shadow: none;
  cursor: not-allowed;
  transform: none;
}

.tag {
  display: inline-flex;
  align-items: center;
  min-height: 26px;
  padding: 3px 10px;
  border-radius: 999px;
  background: var(--color-surface-soft);
  color: var(--color-primary);
  font-size: 12px;
  font-weight: 800;
  white-space: nowrap;
}

.tag.info {
  color: var(--color-info);
  background: #EAF1FF;
}

.tag.warning {
  color: #A15C00;
  background: #FFF4DE;
}

.tag.disabled {
  color: var(--color-muted);
  background: #F3F4F6;
}

.panel,
.game-card {
  background: var(--color-surface);
  border: 1px solid rgba(230, 221, 243, 0.92);
  border-radius: var(--radius-card);
  box-shadow: var(--shadow-card);
}

.panel {
  padding: 24px;
}

.muted {
  color: var(--color-muted);
}

.field {
  min-height: 44px;
  width: 100%;
  border: 1px solid #D8CCE9;
  border-radius: var(--radius-control);
  padding: 10px 12px;
  color: var(--color-text);
  font: inherit;
  font-size: 16px;
  outline: none;
  background: #fff;
}

.field:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(116, 85, 176, 0.14);
}

.feedback {
  border-radius: var(--radius-card);
  border: 1px solid var(--color-border);
  padding: 16px;
  background: #fff;
}

.feedback.success {
  border-color: rgba(34, 160, 107, 0.35);
  background: rgba(34, 160, 107, 0.08);
  color: #176C4A;
}

.feedback.error {
  border-color: rgba(229, 72, 77, 0.35);
  background: rgba(229, 72, 77, 0.08);
  color: #9D2E31;
}

.feedback.info {
  border-color: rgba(79, 127, 217, 0.32);
  background: rgba(79, 127, 217, 0.08);
  color: #315B9D;
}

.app-footer {
  width: min(100% - 32px, var(--page-width));
  margin: 18px auto 0;
  padding: 0 0 32px;
  color: var(--color-muted);
  font-size: 14px;
  text-align: center;
}

.app-footer span,
.app-footer small {
  display: block;
}

.app-footer small {
  margin-top: 4px;
  font-size: 12px;
  line-height: 1.4;
}

@media (max-width: 767px) {
  .app-page,
  .lesson-page {
    width: min(100% - 24px, var(--page-width));
    padding-top: 22px;
  }

  .site-topbar {
    grid-template-columns: 1fr auto;
    align-items: start;
    gap: 10px 12px;
  }

  .site-topbar h1 {
    grid-column: 1 / -1;
    grid-row: 2;
    text-align: left;
    font-size: 22px;
  }

  .site-topbar .tag {
    justify-self: end;
  }

  .btn,
  button.btn,
  a.btn {
    padding-inline: 12px;
    font-size: 14px;
  }

  .site-topbar .btn {
    min-height: 34px;
    padding: 6px 10px;
    font-size: 13px;
  }

  .panel {
    padding: 18px;
  }
}