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

:root {
  --primary: #e63946;
  --primary-light: #ff6b6b;
  --primary-dark: #c1121f;
  --bg: #fdf0d5;
  --bg-card: #ffffff;
  --text: #2b2d42;
  --text-light: #6c757d;
  --accent: #457b9d;
  --accent-light: #a8dadc;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 4px 20px rgba(0, 0, 0, 0.12);
  --radius: 12px;
  --radius-sm: 8px;
  --transition: 0.2s ease;
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC',
    'Hiragino Sans GB', 'Microsoft YaHei', sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.5;
}

/* Header */
.header {
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  color: #fff;
  text-align: center;
  padding: 1.25rem 1rem;
  box-shadow: var(--shadow-lg);
  position: sticky;
  top: 0;
  z-index: 10;
}

.header h1 {
  font-size: 1.4rem;
  font-weight: 700;
  letter-spacing: 0.05em;
}

.header p {
  font-size: 0.85rem;
  opacity: 0.85;
  margin-top: 0.2rem;
}

/* Main container */
.container {
  max-width: 480px;
  margin: 0 auto;
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

/* Card style */
.card {
  background: var(--bg-card);
  border-radius: var(--radius);
  padding: 1.25rem;
  box-shadow: var(--shadow);
}

.card-title {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-light);
  margin-bottom: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

/* Chain area */
.chain-area {
  min-height: 3.5rem;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.4rem;
}

.chain-empty {
  color: var(--text-light);
  font-size: 0.95rem;
  width: 100%;
  text-align: center;
  padding: 0.5rem 0;
}

.chain-pill {
  display: inline-flex;
  align-items: center;
  background: linear-gradient(135deg, var(--accent), var(--accent-light));
  color: #fff;
  border: none;
  border-radius: 2rem;
  padding: 0.4rem 0.9rem;
  font-size: 0.95rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
  font-family: inherit;
}

.chain-pill:hover {
  transform: scale(1.05);
  box-shadow: 0 2px 8px rgba(69, 123, 157, 0.4);
}

.chain-pill:active {
  transform: scale(0.95);
}

.chain-arrow {
  color: var(--text-light);
  font-size: 1rem;
  user-select: none;
}

/* Result area */
.result-area {
  text-align: center;
  transition: all 0.3s ease;
}

.result-area.has-result {
  padding: 1.5rem 1.25rem;
}

.result-default {
  color: var(--text-light);
  font-size: 0.95rem;
  padding: 1rem 0;
}

.result-term {
  font-size: 2.5rem;
  font-weight: 800;
  color: var(--primary);
  transition: all 0.3s ease;
  line-height: 1.3;
  word-break: keep-all;
}

.result-term.not-found {
  font-size: 1.1rem;
  color: var(--text-light);
  font-weight: 500;
}

.result-explanation {
  font-size: 0.9rem;
  color: var(--text-light);
  margin-top: 0.5rem;
}

/* Relationship buttons grid */
.buttons-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 0.5rem;
}

.rel-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-card);
  border: 2px solid #e9ecef;
  border-radius: var(--radius-sm);
  padding: 0.75rem 0.25rem;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text);
  cursor: pointer;
  transition: all var(--transition);
  font-family: inherit;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.rel-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
  transform: translateY(-1px);
  box-shadow: 0 2px 8px rgba(230, 57, 70, 0.15);
}

.rel-btn:active {
  transform: scale(0.93);
  border-color: var(--primary-dark);
  background: #fff5f5;
}

/* Control buttons */
.controls {
  display: flex;
  gap: 0.75rem;
}

.ctrl-btn {
  flex: 1;
  padding: 0.75rem;
  border: 2px solid #e9ecef;
  border-radius: var(--radius-sm);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  font-family: inherit;
  -webkit-tap-highlight-color: transparent;
}

.ctrl-btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.ctrl-btn--undo {
  background: #fff;
  color: var(--accent);
  border-color: var(--accent-light);
}

.ctrl-btn--undo:not(:disabled):hover {
  background: var(--accent);
  color: #fff;
}

.ctrl-btn--undo:not(:disabled):active {
  transform: scale(0.96);
}

.ctrl-btn--reset {
  background: #fff;
  color: var(--primary);
  border-color: #ffccd5;
}

.ctrl-btn--reset:not(:disabled):hover {
  background: var(--primary);
  color: #fff;
}

.ctrl-btn--reset:not(:disabled):active {
  transform: scale(0.96);
}

/* Footer */
.footer {
  text-align: center;
  padding: 1.5rem 1rem;
  color: var(--text-light);
  font-size: 0.75rem;
}

/* Responsive */
@media (max-width: 360px) {
  .buttons-grid {
    grid-template-columns: repeat(4, 1fr);
  }

  .result-term {
    font-size: 2rem;
  }
}

@media (min-width: 481px) {
  .container {
    padding: 1.5rem;
  }

  .header {
    padding: 1.5rem 1rem;
  }

  .header h1 {
    font-size: 1.6rem;
  }
}

/* Smooth transitions for dynamic elements */
.chain-pill,
.result-term,
.result-explanation {
  transition: opacity 0.25s ease, transform 0.25s ease;
}