* {
  box-sizing: border-box;
  font-family: "Poppins", sans-serif;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: var(--bg);
  transition: 0.3s;
}

/* Default (Light Theme) */
:root {
  --bg: #f4f5f8;
  --button-bg: #ffffff;
  --button-hover: #e5e8ee;
  --display-bg: #1a1f2b;
  --display-color: #ffffff;
  --operator-bg: #0d6efd;
  --operator-color: #fff;
  --equal-bg: #198754;
  --equal-color: #fff;
  --text-color: #222;
  --special-bg: #dc3545;
  --special-color: #fff;
}

/* Dark Theme */
body.dark {
  --bg: #181818;
  --button-bg: #2a2a2a;
  --button-hover: #3a3a3a;
  --display-bg: #000;
  --display-color: #00ff99;
  --operator-bg: #007bff;
  --operator-color: #fff;
  --equal-bg: #00c853;
  --equal-color: #fff;
  --text-color: #f4f4f4;
  --special-bg: #ff3b30;
  --special-color: #fff;
}

.calculator-container {
  width: 340px;
  padding: 15px;
  border-radius: 15px;
  box-shadow: 0 5px 25px rgba(0, 0, 0, 0.2);
  background: var(--button-bg);
  transition: 0.3s;
}

.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  margin-bottom: 8px;
}

.theme-label {
  color: var(--text-color);
  margin-left: 6px;
  font-size: 0.9rem;
}

.switch {
  position: relative;
  display: inline-block;
  width: 45px;
  height: 22px;
}

.switch input {
  opacity: 0;
  width: 0;
  height: 0;
}

.slider {
  position: absolute;
  cursor: pointer;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: #ccc;
  border-radius: 22px;
  transition: 0.3s;
}

.slider:before {
  position: absolute;
  content: "";
  height: 18px;
  width: 18px;
  left: 2px;
  bottom: 2px;
  background-color: white;
  border-radius: 50%;
  transition: 0.3s;
}

input:checked + .slider {
  background-color: #2196f3;
}

input:checked + .slider:before {
  transform: translateX(23px);
}

/* Display */
.display input {
  width: 100%;
  height: 50px;
  font-size: 1.5rem;
  border: none;
  outline: none;
  text-align: right;
  padding: 10px;
  border-radius: 10px;
  color: var(--display-color);
  background: var(--display-bg);
  margin-bottom: 12px;
}

/* Buttons Grid */
.buttons {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
}

button {
  height: 42px;
  font-size: 0.95rem;
  border: none;
  border-radius: 8px;
  background: var(--button-bg);
  color: var(--text-color);
  cursor: pointer;
  transition: 0.2s;
}

button:hover {
  background: var(--button-hover);
}

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

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

.ac {
  background: var(--special-bg);
  color: var(--special-color);
}

.mode {
  background: #ffc107;
  color: #000;
  font-weight: 600;
}