:root {
  --bg-color: #ffffff;
  --text-color: #000000;
  --btn-bg: #e0e0e0;
  --btn-text: #000000;
}

body.dark-mode {
  --bg-color: #121212;
  --text-color: #ffffff;
  --btn-bg: #333333;
  --btn-text: #ffffff;
}

body {
  background-color: var(--bg-color);
  color: var(--text-color);
  transition: background-color 0.3s, color 0.3s;
  font-family: sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
}

button {
  background-color: var(--btn-bg);
  color: var(--btn-text);
  border: none;
  padding: 10px 20px;
  cursor: pointer;
  border-radius: 5px;
  transition: background-color 0.3s, color 0.3s;
}

button:hover {
  opacity: 0.8;
}