* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
  }
  
  body {
    font-family: "Helvetica Neue", sans-serif;
    width: 100vw;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
  }
  
  .calculator {
    background: black;
    border-radius: 50px;
    color: white;
    height: 800px;
    width: 80%;
    max-width: 500px;
    padding: 1rem;
    display: flex;
    flex-direction: column;
    align-items: center;
  }
  
  .display {
    height: 15rem;
    width: 100%;
    text-align: right;
    padding: 1rem;
    font-size: 4rem;
    display: flex;
    flex-direction: column;
    justify-content: space-evenly;
  }
  .previous-display {
    opacity: 0.5;
    font-size: 1.5rem;
    overflow: hidden;
  }
  
  .buttons-container {
    width: 100%;
    display: grid;
    grid-gap: 0.5rem;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(5, 1fr);
  }
  
  .button {
    display: flex;
    align-items: center;
    justify-content: center;
    background: #333;
    border-radius: 50%;
    cursor: pointer;
    font-size: 3rem;
    height: 6rem;
    width: 6rem;
    transition: filter 0.3s;
  }
  
  .button.function {
    color: black;
    background: #a5a5a5;
  }
  
  .button.operator {
    background: #f1a33c;
  }
  
  .button.number-0 {
    border-radius: 3rem;
    grid-column: 1 / span 2;
    justify-content: flex-start;
    padding-left: 2rem;
    width: 12rem;
  }
  
  .button:hover {
    opacity: 0.5;
  }
  
  @media screen and (max-width: 576px) {
    .calculator {
      width: 350px;
      height: 600px;
    }
    .display {
      height: 10rem;
      font-size: 3rem;
    }
  
    .button {
      font-size: 1.7rem;
      height: 4rem;
      width: 4rem;
    }
    .button.number-0 {
      border-radius: 2rem;
      padding-left: 1.3rem;
      width: 8rem;
    }
  }