:root[data-theme="light"] {
  --bg: #ffffff;
  --text: #000000;
  --box: #f5f5f5;
  --link: #0047ab;
  --accent: #111111;
  --star-color: #222222;
}

:root[data-theme="dark"] {
  --bg: #0d1117;
  --text: #ffffff;
  --box: #161b22;
  --link: #58a6ff;
  --accent: #ccc;
  --star-color: #58a6ff;
}

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: 'Inter', sans-serif;
  transition: background 0.3s, color 0.3s;
}

canvas#stars {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  z-index: -1;
  pointer-events: none;
  background: transparent;
}

.container {
  max-width: 600px;
  margin: 2rem auto;
  padding: 2rem;
  background-color: var(--box);
  border-radius: 12px;
  box-shadow: 0 0 25px rgba(0, 0, 0, 0.2);
  z-index: 1;
  position: relative;
}

h1 {
  text-align: center;
  font-size: 2rem;
  color: var(--link);
  margin-bottom: 1.5rem;
}

.button-group {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
  margin-bottom: 1rem;
}

button {
  padding: 0.5rem 1rem;
  font-size: 1rem;
  border: none;
  border-radius: 6px;
  background-color: var(--link);
  color: var(--bg);
  cursor: pointer;
  font-weight: 600;
  transition: opacity 0.2s ease;
}

button:hover {
  opacity: 0.9;
}

input[type="text"] {
  width: 100%;
  padding: 0.6rem 1rem;
  font-size: 1rem;
  border: 2px solid var(--link);
  border-radius: 8px;
  background: transparent;
  color: var(--text);
  margin-bottom: 1rem;
}

.todo-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
  margin-bottom: 1rem;
}

ul#todo-list {
  list-style: none;
  padding: 0;
}

ul#todo-list li {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: transparent;
  border: 1px solid var(--link);
  color: var(--link);
  padding: 0.5rem 1rem;
  margin-bottom: 0.5rem;
  border-radius: 8px;
}

ul#todo-list li button {
  color: #ff6b6b;
  background: none;
  border: none;
  font-size: 1.2rem;
  cursor: pointer;
}

ul#todo-list li button:hover {
  color: red;
}

/* Responsive layout */
@media (max-width: 600px) {
  .button-group {
    flex-direction: column;
    align-items: center;
  }

  .todo-controls {
    flex-direction: column;
    align-items: center;
  }
}