@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@400;600&display=swap');

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: 'Poppins', sans-serif;
  background: linear-gradient(135deg, #667eea, #764ba2);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  transition: background 0.3s ease;
}

.top-bar {
  position: absolute;
  top: 20px;
  right: 20px;
}

#theme-toggle {
  padding: 10px 15px;
  font-size: 0.9rem;
  border: none;
  border-radius: 20px;
  background: #ffffffcc;
  cursor: pointer;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
  transition: background 0.3s ease;
}

#theme-toggle:hover {
  background: #ffffffee;
}

.calculator {
  background: #ffffff;
  padding: 25px;
  border-radius: 20px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.2);
  width: 90%;
  max-width: 360px;
}

#display {
  width: 100%;
  height: 60px;
  font-size: 1.8rem;
  text-align: right;
  margin-bottom: 20px;
  padding: 12px;
  border-radius: 12px;
  border: none;
  background-color: #f9f9f9;
  box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.1);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

button {
  font-size: 1.2rem;
  padding: 15px;
  border: none;
  border-radius: 12px;
  background: #f1f1f1;
  cursor: pointer;
  transition: background 0.2s, transform 0.1s;
}

button:hover {
  background: #e0e0e0;
  transform: translateY(-2px);
}

.equal {
  grid-column: span 2;
  background: #4caf50;
  color: white;
}

.equal:hover {
  background: #43a047;
}

body.dark {
  background: linear-gradient(135deg, #232526, #414345);
}

body.dark .calculator {
  background: #2c2c2c;
  color: white;
}

body.dark #display {
  background-color: #3a3a3a;
  color: white;
}

body.dark button {
  background: #444;
  color: white;
}

body.dark button:hover {
  background: #555;
}

body.dark .equal {
  background: #00c853;
}

body.dark .equal:hover {
  background: #00b248;
}

button.active-key {
  background-color: #ccc !important;
  transform: scale(0.98);
}

body.dark button.active-key {
  background-color: #666 !important;
}

@media screen and (max-width: 480px) {
  #display {
    height: 50px;
    font-size: 1.5rem;
  }

  button {
    padding: 12px;
    font-size: 1rem;
  }
}