:root {
  --bg-primary: #0a0d16;
  --bg-surface: #141b2a;
  --bg-card: #1c2538;
  --text-main: #f0f6fc;
  --text-muted: #8b949e;
  --border-subtle: #2d3848;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg-primary);
  color: var(--text-main);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
.site-header { background: var(--bg-surface); border-bottom: 1px solid var(--border-subtle); padding: 0.75rem 1.25rem; }
.header-inner { max-width: 1000px; margin: 0 auto; display: flex; align-items: center; justify-content: space-between; }
.back-link { color: var(--text-muted); text-decoration: none; font-size: 0.95rem; }
.back-link:hover { color: #58a6ff; }
.logo-area { display: flex; align-items: center; gap: 0.5rem; font-weight: 600; }
.icon-button { background: var(--bg-card); border: 1px solid var(--border-subtle); color: #fff; padding: 0.5rem 0.75rem; border-radius: 8px; cursor: pointer; min-width: 44px; min-height: 44px; }
.game-container { max-width: 760px; margin: 1.5rem auto; padding: 0 1rem; flex: 1; display: flex; flex-direction: column; align-items: center; }
.game-header-text { text-align: center; margin-bottom: 1rem; }
.game-title { font-size: 1.75rem; font-weight: 800; margin-bottom: 0.35rem; color: #fff; }
.game-subtitle { color: var(--text-muted); font-size: 0.95rem; }
.hud-bar { display: flex; flex-wrap: wrap; gap: 1.5rem; background: var(--bg-surface); border: 1px solid var(--border-subtle); border-radius: 12px; padding: 0.75rem 1.5rem; margin-bottom: 1.5rem; justify-content: center; }
.hud-item { display: flex; flex-direction: column; align-items: center; }
.hud-label { font-size: 0.75rem; text-transform: uppercase; color: var(--text-muted); font-weight: 600; }
.hud-val { font-size: 1.35rem; font-weight: 800; color: #fff; }
.hud-val.timer { color: #f85149; }
.math-card {
  position: relative;
  width: 100%;
  max-width: 500px;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: 16px;
  padding: 2rem 1.5rem;
  box-shadow: 0 12px 36px rgba(0,0,0,0.5);
  margin-bottom: 1.5rem;
  text-align: center;
}
.equation-display {
  font-size: 2.5rem;
  font-weight: 900;
  color: #fff;
  letter-spacing: 2px;
  margin-bottom: 1.5rem;
}
.answers-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
.ans-btn {
  background: var(--bg-card);
  border: 2px solid var(--border-subtle);
  border-radius: 12px;
  color: #fff;
  font-size: 1.65rem;
  font-weight: 800;
  padding: 1rem;
  cursor: pointer;
  transition: transform 0.1s ease, border-color 0.15s ease;
  min-height: 64px;
}
.ans-btn:hover { border-color: #58a6ff; }
.ans-btn:active { transform: translateY(2px); }
.ans-btn.correct { background: #238636; border-color: #2ea043; }
.ans-btn.wrong { background: #da3633; border-color: #f85149; }
.start-cover {
  position: absolute;
  inset: 0;
  background: rgba(20, 27, 42, 0.96);
  border-radius: 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
}
.start-cover.hidden { display: none; }
.start-cover h2 { font-size: 1.5rem; color: #fff; margin-bottom: 0.5rem; }
.start-cover p { color: var(--text-muted); margin-bottom: 1.25rem; }
.btn-primary { background: #238636; color: #fff; border: none; padding: 0.75rem 1.75rem; font-weight: 700; border-radius: 8px; cursor: pointer; font-size: 1rem; min-height: 44px; }
.content-block { max-width: 760px; width: 100%; background: var(--bg-surface); border: 1px solid var(--border-subtle); border-radius: 12px; padding: 1.75rem; line-height: 1.7; }
.article-header { border-bottom: 1px solid var(--border-subtle); padding-bottom: 1rem; margin-bottom: 1rem; }
.article-header h2 { font-size: 1.35rem; color: #fff; }
.article-meta { color: var(--text-muted); font-size: 0.85rem; }
.article-section { margin-bottom: 1.25rem; }
.article-section h3 { font-size: 1.1rem; color: #58a6ff; margin-bottom: 0.5rem; }
.article-section p { color: #c9d1d9; margin-bottom: 0.65rem; }
.article-section ul { padding-left: 1.5rem; color: #c9d1d9; margin-bottom: 0.65rem; }
.faq-accordion { display: flex; flex-direction: column; gap: 0.65rem; }
.faq-item { background: var(--bg-card); border: 1px solid var(--border-subtle); border-radius: 8px; padding: 0.75rem 1rem; }
.faq-question { font-weight: 600; cursor: pointer; color: #fff; }
.faq-answer { margin-top: 0.5rem; color: #8b949e; }
.modal-overlay { position: fixed; inset: 0; background: rgba(0,0,0,0.8); display: flex; align-items: center; justify-content: center; z-index: 100; }
.modal-overlay.hidden { display: none; }
.modal-card { background: var(--bg-surface); border: 1px solid var(--border-subtle); padding: 2rem; border-radius: 16px; text-align: center; max-width: 360px; width: 100%; }
.modal-badge { font-size: 3rem; margin-bottom: 0.5rem; }
.site-footer { background: var(--bg-surface); border-top: 1px solid var(--border-subtle); padding: 1.5rem; text-align: center; color: var(--text-muted); font-size: 0.85rem; margin-top: auto; }