style.css

/* insialize css */
* {
  margin: 0;
  padding: 0;
  font-family: Gotham Rounded, sans-serif;
  font-weight: normal;
  box-sizing: border-box;
}
/* body css */
body {
  background: rgb(131, 58, 180);
  background: linear-gradient(
    90deg,
    rgba(131, 58, 180, 1) 0%,
    rgba(253, 29, 29, 1) 50%,
    rgba(252, 176, 69, 1) 100%
  );
}
/* calculator css */
.container {
  width: 100%;
  height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}
/* calculator css */
.calculator {
  border: 1px solid #fff;
  width: 400px;
  height: 500px;
  border-radius: 30px;
  overflow: hidden;
}
/* calculator title css */
h1 {
  color: #fff;
  font-size: 2rem;
  text-align: center;
  padding: 10px;
  font-family: "Courier New", Courier, monospace;
}
/* calculator head css */
.calculatorHead {
  width: 100%;
  height: 20%;
  background: #c4c4c4;
  display: flex;
  justify-content: flex-end;
  align-items: flex-end;
  flex-direction: column;
  padding: 10px;
}
/* calculator preview value css */
.calculatorHead .previous-value {
  color: rgb(255, 255, 255);
  font-size: 1.5rem;
  height: 50%;
}
/* calculator current value css */
.calculatorHead .current-value {
  color: black;
  font-size: 2rem;
  height: 50%;
}
/* calculator body css */
.calculatorBody {
  width: 100%;
  height: 80%;
  background: #fff;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-gap: 20px;
  padding: 15px;
}
/* calculator buttons css */
.calculatorBody .grid-item {
  background-color: #fff;
  border: 1px solid #c4c4c4;
  border-radius: 30px;
  font-size: 2rem;
  color: #333;
  text-align: center;
}
.calculatorBody .grid-item:hover {
  background-color: #eaeaea;
}
button:last-child {
  grid-column: 2 / 5;
}