style.css

@import url('https://fonts.googleapis.com/css2?family=Orbitron:wght@400;500;600;700;800;900&display=swap');

html {
  box-sizing: border-box;
}

*,
*::before,
*::after {
  box-sizing: inherit;
}

body {
  margin: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 0 1.5em;
  font-family: 'Orbitron', sans-serif;
}

button {
  cursor: pointer;
  border-radius: 1em;
  height: 45px;
  width: 45px;
  border: none;
  border-radius: 50%;
}

.calculator {
  background-color: #1c1c1c;
  padding: 1.5em;
  border-radius: 1em;
  max-width: 70vw;
  box-shadow: rgba(0, 0, 0, 0.35) 0px 5px 15px;
}

.display {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  flex-wrap: wrap;

  background-color: #505050;
  border-radius: 20px;
  padding: 0 10px;
  height: 80px;
  font-size: 2rem;
  margin-bottom: 20px;
  width: 100%;
  color: #fff;
}

.buttons__utility {
  display: flex;
  margin-bottom: 1.5em;
}

.buttons__utility button {
  width: 60px;
  border-radius: 1.5em;
  margin: 0.15em;
}

.buttons__math {
  display: flex;
}

.buttons__math button {
  aspect-ratio: 1;
}

.buttons__numbers {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-around;
  max-width: 150px;
}

.number {
  margin: 0.15em;
}

.button__equals {
  margin: 0.15em;
  font-size: 1.2rem;
}

.buttons__operators {
  display: flex;
  flex-direction: column;
}

.operator {
  background-color: #ff9500;
  font-size: 1.2rem;
  margin: 0.15em;
}

@media (prefers-color-scheme: dark) {
  body {
    background-color: #1b1b1b;
  }

  .calculator {
    background-color: black;
  }

  button {
    background-color: #1b1b1b;
    color: white;
  }
}

@media screen and (min-width: 768px) {
  .display {
    max-width: 25vw;
  }
}