:root {
  --color-bg: #f7f7f9;
  --color-text: #1f1f1f;
  --color-muted: #6b6b6b;
  --color-accent: #3b5bfd;
  --color-card-bg: #ffffff;
  --color-border: #e3e3e8;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Hiragino Kaku Gothic ProN", "Yu Gothic", -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
}

.timer-app {
  max-width: 420px;
  margin: 2rem auto 4rem;
  padding: 2.5rem;
  background: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: 16px;
  text-align: center;
}

.timer-app h1 {
  margin: 0 0 0.5rem;
  font-size: 1.5rem;
}

.description {
  margin: 0 0 2rem;
  color: var(--color-muted);
  font-size: 0.9rem;
}

.time-display {
  font-size: 3.5rem;
  font-variant-numeric: tabular-nums;
  font-weight: 600;
  letter-spacing: 0.05em;
}

.current-interval {
  margin: 0.5rem 0 2rem;
  color: var(--color-muted);
  font-size: 0.9rem;
  font-variant-numeric: tabular-nums;
}

.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
  margin-bottom: 2rem;
}

.btn {
  padding: 0.75rem 1.75rem;
  border-radius: 999px;
  border: 1px solid var(--color-border);
  background: #fff;
  color: var(--color-text);
  font-size: 1rem;
  cursor: pointer;
  transition: transform 0.1s ease, background 0.15s ease;
}

.btn:hover {
  background: #f0f0f4;
}

.btn:active {
  transform: scale(0.97);
}

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

.btn-primary:hover {
  background: #2f4bd9;
}

.btn-small {
  padding: 0.4rem 0.9rem;
  font-size: 0.85rem;
}

.settings {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.setting-group {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.6rem;
}

.setting-label {
  margin: 0;
  color: var(--color-muted);
  font-size: 0.9rem;
}

.interval-list {
  list-style: none;
  margin: 0;
  padding: 0;
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.interval-row {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.5rem 0.75rem;
  border: 1px solid var(--color-border);
  border-radius: 8px;
  background: #fff;
}

.interval-row.active {
  border-color: var(--color-accent);
  background: #eef1ff;
}

.interval-row input[type="number"] {
  width: 4.5rem;
  padding: 0.35rem 0.5rem;
  border-radius: 6px;
  border: 1px solid var(--color-border);
  font-size: 0.95rem;
  text-align: right;
}

.interval-row .unit {
  color: var(--color-muted);
  font-size: 0.9rem;
}

.remove-btn {
  margin-left: auto;
  width: 1.75rem;
  height: 1.75rem;
  border-radius: 50%;
  border: 1px solid var(--color-border);
  background: #fff;
  color: var(--color-muted);
  font-size: 1rem;
  line-height: 1;
  cursor: pointer;
}

.remove-btn:hover:not(:disabled) {
  background: #fde8e8;
  color: #c0392b;
  border-color: #f3b8b8;
}

.remove-btn:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

.setting-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  justify-content: center;
  color: var(--color-muted);
  font-size: 0.9rem;
}

.setting-row select {
  padding: 0.4rem 0.6rem;
  border-radius: 8px;
  border: 1px solid var(--color-border);
  background: #fff;
  color: var(--color-text);
  font-size: 0.9rem;
}

.setting-row input[type="range"] {
  flex: 1;
  max-width: 160px;
}

#volumeValue {
  min-width: 2ch;
  text-align: right;
  font-variant-numeric: tabular-nums;
}