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

body {
  background-color: #000;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  font-family: -apple-system, BlinkMacSystemFont, sans-serif;
}

.calculator {
  background-color: #000;
  border-radius: 40px;
  overflow: hidden;
  width: 320px;
  padding: 20px 10px;
}

.display {
  color: white;
  font-size: 4rem;
  text-align: right;
  padding: 20px 10px;
  min-height: 80px;
}

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

/* Button base style */
.btn {
  font-size: 2rem;
  padding: 20px 0;
  border: none;
  border-radius: 50%;
  cursor: pointer;
  width: 70px;
  height: 70px;
  display: flex;
  justify-content: center;
  align-items: center;
  transition: filter 0.2s;
}

/* Button types */
.number {
  background-color: #bb00ff;
  color: white;
}

.operator {
  background-color: #00ffd9;
  color: black;
}

.utility {
  background-color: #808080;
  color: black;
}

.equals {
  background-color: #00ffd9;
  color: black;
}


.zero {
  grid-column: span 2;
  border-radius: 35px;
  justify-content: flex-start;
  padding-left: 28px;
  width: 150px;
}

.btn:hover {
  filter: brightness(5);
}