:root {
  --bg: #f5f5f5;
  --fg: #333;
  --primary: #0066cc;
  --accent: #cc6600;
}
body.dark {
  --bg: #222;
  --fg: #eee;
  --primary: #3399ff;
  --accent: #ff9933;
}

* { box-sizing: border-box; }
body {
  margin: 0; padding: 0;
  font-family: Arial, sans-serif;
  background: var(--bg);
  color: var(--fg);
}
header {
  background: var(--primary);
  color: #fff;
  padding: 1rem;
  text-align: center;
}
nav {
  margin-top: 0.5rem;
}
nav button {
  background: transparent;
  border: none;
  color: #fff;
  font-size: 1rem;
  margin: 0 0.5rem;
  padding: 0.5rem;
  cursor: pointer;
}
nav button.active {
  border-bottom: 2px solid #fff;
}

main {
  max-width: 800px;
  margin: 1.5rem auto;
  padding: 1rem;
  background: var(--bg);
}
.tab-content.hidden { display: none; }

form {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr auto;
  gap: 0.5rem;
  margin-bottom: 1rem;
}
form input, form select, form button {
  padding: 0.5rem;
  font-size: 1rem;
}

#task-list, #history-list {
  list-style: none;
  padding: 0;
  margin: 0 0 1rem 0;
}
#task-list li, #history-list li {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem;
  border-bottom: 1px solid #ddd;
  background: var(--bg);
}
#task-list li.due { background: var(--accent); color: #fff; }

#timer {
  text-align: center;
}
#timer-display { font-size: 2rem; margin-bottom: 0.5rem; display: block; }
#timer button {
  padding: 0.5rem 1rem;
  font-size: 1rem;
  margin: 0 0.25rem;
}

.setting-item {
  margin: 1rem 0;
}