styles.css

:root {
  --primary-bg: #ffffff;
  --primary-text: #000000;
  --secondary-bg: #222222;
  --secondary-text: #ffffff;
  --btn-bg: #e0e0e0;
  --btn-hover-bg: #d0d0d0;
  --operator-bg: #ff9500;
  --operator-hover-bg: #e68a00;
  --clear-bg: #f44336;
  --clear-hover-bg: #d32f2f;
  --backspace-bg: #ff5722;
  --backspace-hover-bg: #e64a19;
}

[data-theme="dark"] {
  --primary-bg: #121212;
  --primary-text: #e0e0e0;
  --secondary-bg: #424242;
  --secondary-text: #ffffff;
  --btn-bg: #424242;
  --btn-hover-bg: #616161;
  --operator-bg: #ff9800;
  --operator-hover-bg: #fb8c00;
  --clear-bg: #e53935;
  --clear-hover-bg: #c62828;
  --backspace-bg: #d84315;
  --backspace-hover-bg: #bf360c;
}

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

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

.calculator {
  background-color: var(--primary-bg);
  border-radius: 10px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.1);
  width: 350px;
  padding: 20px;
}

.display {
  background-color: var(--secondary-bg);
  color: var(--secondary-text);
  font-size: 2.5em;
  padding: 20px;
  border-radius: 10px;
  text-align: right;
  margin-bottom: 20px;
  user-select: none;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.btn {
  padding: 20px;
  font-size: 1.5em;
  border: none;
  border-radius: 10px;
  background-color: var(--btn-bg);
  color: var(--primary-text);
  cursor: pointer;
  transition: background-color 0.3s;
}

.btn:hover {
  background-color: var(--btn-hover-bg);
}

.btn[data-type="operator"] {
  background-color: var(--operator-bg);
  color: var(--secondary-text);
}

.btn[data-type="operator"]:hover {
  background-color: var(--operator-hover-bg);
}

.btn[data-type="clear"] {
  background-color: var(--clear-bg);
  color: var(--secondary-text);
}

.btn[data-type="clear"]:hover {
  background-color: var(--clear-hover-bg);
}

.btn[data-type="backspace"] {
  background-color: var(--backspace-bg);
  color: var(--secondary-text);
}

.btn[data-type="backspace"]:hover {
  background-color: var(--backspace-hover-bg);
}

.btn[data-type="equal"] {
  grid-column: span 1;
}

.theme-toggle {
  margin-bottom: 20px;
}

.theme-toggle button {
  padding: 10px 20px;
  font-size: 1em;
  border: none;
  border-radius: 5px;
  background-color: var(--btn-bg);
  color: var(--primary-text);
  cursor: pointer;
  transition: background-color 0.3s, color 0.3s;
}

.theme-toggle button:hover {
  background-color: var(--btn-hover-bg);
}