html {
    box-sizing: border-box;
}
*, *:before, *:after {
    box-sizing: inherit;
}
body {
  padding: 0;
  margin: 0;
}
.wrapper {
    width: 400px;
}

.calculator-screen {
    background: black;
    color: white;
    text-align: right;
    padding: 20px;
}

.previousOperand {
    font-size: 1.2rem;
    opacity: 0.7;
}

.currentOperand {
    font-size: 2.5rem;
    opacity: 0.7;
}

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

.button {
  height: 80px;
  font-size: 1.5rem;
  border: 1px solid black;
  cursor: pointer;
}

.operator, .equals {
    background: orange;
    color: white;
}

.span-2 {
    grid-column: span 2;
}

.span-3 {
    grid-column: span 3;
}

.button:hover {
    opacity: 0.8;
}

.button:active {
    transform: scale(0.95);
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
}