body {
  /* Used for fonts and general background */
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto;
  background: #333;
  margin: 0;
  display: flex; /* for centering */
  align-items: center;
  justify-content: center;
  height: 100vh;
}
.calculator {
  margin-top: 10px;
  width: 320px;
  background: #222;
  border-radius: 30px;
  overflow: hidden;
  min-height: 500px;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.170);
}
.display {
  background: #1c1c1c;
  color: white; /* text color */
  font-size: 2rem;
  text-align: right;
  padding: 20px 10px;
  height: 80px;
}
.buttons {
  display: grid; /* creates grid layout */
  grid-template-columns: repeat(4, 1fr);
  gap: 5px;
  background: #444;
  padding: 10px;
}
.button {
  background: #555;
  border: none;
  padding: 20px;
  font-size: 1.5rem;
  color: white; /* default text color */
  cursor: pointer;
  border-radius: 30px;
  outline: none; /* Remove outline (desktop) */
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.170);
  transition: transform 0.1s;
}
/* increase size on hover */
.button:hover {
  transform: scale(1.08);
}
.button:active {
  background-color: #303030;
  transform: scale(1);
}
.operator {
  background: #ffa009;
  /* operator button color */
}
.operator:active {
  background-color: #cc8000;
  /* color change when active */
  transform: scale(1);
}
.zero {
  grid-column: span 2;
}
.clear:hover {
  background: #ff4c4c;
}
* {
  /* Disables highlighting on tap (mobile)*/
  -webkit-tap-highlight-color: transparent;
}