styles.css

*,
*::before,
*::after {
  box-sizing: border-box;
  font-family: Arial, Helvetica, sans-serif;
  font-weight: normal;
}

body {
  margin: 0;
  padding: 0;
  background: rgb(34, 193, 195);
  background: linear-gradient(
    103deg,
    rgb(34, 193, 195) 0%,
    rgb(236, 197, 112) 83%
  );
}

.flex {
  display: flex;
}

.grid {
  display: grid;
}

.calculator {
  min-height: 100vh;
  justify-content: center;
  align-content: center;
  grid-template-columns: repeat(4, 100px);
  grid-template-rows: minmax(120px, auto) repeat(5, 100px);

  & button {
    cursor: pointer;
    font-size: 2rem;
    border: 1px solid white;
    outline: none;
    background-color: rgba(255, 255, 255, 0.75);
  
    &:hover {
      background-color: rgba(255, 255, 255, 0.9);
    }
  }
}

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

.output {
  grid-column: 1/-1;
  background-color: rgba(0, 0, 0, 0.75);
  justify-content: space-around;
  align-items: flex-end;
  flex-direction: column;
  padding: 10px;
  word-wrap: break-word;
  word-break: break-all;

  .previous-operand {
    color: rgba(255, 255, 255, 0.75);
    font-size: 1.5rem;
  }

  .current-operand {
    color: white;
    font-size: 2.5rem;
  }
}