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

:root {
  --background-color: #0f0f0f;
  --button-color: #282828;
  --number-color: #f2f2f2;
  --function-button-color: #4a4a4a;
  --highlight-hover-color: #ffcc66;
  --display-background-color: black;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background-color: rgb(169, 230, 230);
}

.calculator {
  max-width: 20rem;
  display: grid;
  background-color: var(--background-color);
  grid-template-columns: repeat(4, 5rem);
  grid-auto-rows: 5rem;
  border-radius: 0.8rem;
  box-shadow: 5px 6px 4px rgba(0, 0, 0, 0.5);
}

.output {
  grid-column: 1 / -1;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  justify-content: flex-end;
  font-size: 1.5rem;
  color: var(--number-color);
  padding-right: 0.8rem;
}

.calculator button {
  border: none;
  cursor: pointer;
  background-color: var(--button-color);
  font-size: 1.3rem;
  font-weight: bold;
  color: var(--number-color);
  transition: 200ms;
}

.calculator > button:hover {
  background-color: var(--highlight-hover-color);
  color: var(--button-color);
}

.calculator button.special-button {
  grid-column: span 2;
  background-color: var(--highlight-hover-color);
  color: var(--button-color);
}