style.css

*,
*::before,
*::after {
  margin: 0;
  padding: 0;
}

:root {
  --number-bg: rgb(51, 51, 51);
  --number-down-bg: rgb(115, 115, 115);

  --operator-bg: rgb(241, 163, 59);
  --operator-down-bg: rgb(243, 200, 149);

  --mono-bg: rgb(165, 165, 165);
  --mono-down-bg: rgb(217, 217, 217);

  --calculator-bg: rgb(0, 0, 0);
  --backdrop-bg: rgb(0, 0, 0, 80%);

  --button-size: 70px;
  --button-spacing: 20px;
  --calculator-padding: 20px;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  width: 100vw;
  font-family: 'Inter', Helvetica, sans-serif;
  font-weight: 200;
  background-color: var(--backdrop-bg);
}

.calculator {
  display: flex;
  width: calc((var(--button-size) + var(--button-spacing)) * 4);
  gap: var(--button-spacing);
  flex-direction: column;
  justify-content: center;
  align-content: center;
  background-color: var(--calculator-bg);
  padding: var(--calculator-padding);
  overflow: none;
  border-radius: 20px;
  filter: drop-shadow(5px 5px 10px #000);
}

.screen {
  background-color: var(--calculator-bg);
  padding-top: 100px;
  color: white;
  text-align: right;
  font-size: 5em;
}

.numpad {
  display: grid;
  grid-template-rows: repeat(5, 1fr);
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

button {
  border-radius: 100000px;
  width: var(--button-size);
  height: var(--button-size);
  border: none;
  font-size: 32px;
  font-weight: 200;
}
button:hover {
  cursor: pointer;
}

button.mono {
  background-color: var(--mono-bg);
}
button.mono:hover {
  background-color: var(--mono-down-bg);
}

button.operator {
  background-color: var(--operator-bg);
  color: white;
}
button.operator:hover {
  background-color: var(--operator-down-bg);
}

button.number {
  background-color: var(--number-bg);
  color: white;
}
button.number:hover {
  background-color: var(--number-down-bg);
}

button.zero {
  grid-column: span 2;
  width: calc(var(--button-size) * 2 + var(--button-spacing));
  text-align: left;
  padding-left: calc((var(--button-size) / 2) - var(--button-spacing) + 0.5rem);
}