body {
  margin: 0;
  height: 100vh;
  background-color: #000a0f;
  background-image:
    repeating-linear-gradient(
      45deg,
      rgba(0, 255, 0, 0.05),
      rgba(0, 255, 0, 0.05) 2px,
      transparent 2px,
      transparent 20px
    ),
    repeating-linear-gradient(
      -45deg,
      rgba(0, 255, 0, 0.05),
      rgba(0, 255, 0, 0.05) 2px,
      transparent 2px,
      transparent 20px
    );
  background-blend-mode: screen;
  display: flex;
  justify-content: center;
  align-items: center;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}


.calculator {
  width: 320px;
  background: #222831;
  border-radius: 15px;
  box-shadow: 0 8px 15px rgba(0,0,0,0.3);
  padding: 20px;
  user-select: none;
}


.display {
  background: #393E46;
  color: #EEEEEE;
  font-size: 2.5rem;
  text-align: right;
  padding: 20px 15px;
  border-radius: 10px;
  margin-bottom: 20px;
  min-height: 60px;
  letter-spacing: 2px;
  overflow-x: auto;
}


.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
}


.buttons button {
  background: #00ADB5;
  border: none;
  border-radius: 12px;
  color: #EEEEEE;
  font-size: 1.5rem;
  font-weight: 600;
  padding: 18px 0;
  cursor: pointer;
  transition: background-color 0.25s ease, transform 0.15s ease;
  box-shadow: 0 4px 8px rgba(0,173,181,0.5);
}


.buttons button:hover {
  background-color: #019ca1;
  transform: translateY(-2px);
}

.buttons button:active {
  background-color: #008b8f;
  transform: translateY(1px);
  box-shadow: none;
}


.buttons button.operator {
  background: #FF5722;
  box-shadow: 0 4px 8px rgba(255, 87, 34, 0.6);
}

.buttons button.operator:hover {
  background: #e64a19;
}

.buttons button.operator:active {
  background: #cc3d16;
  box-shadow: none;
}


.buttons button.operator.C {
  grid-column: span 2;
}


.buttons button.zero {
  grid-column: span 2;
}