*{
    box-sizing: border-box;
}

body{
    margin: 0;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

#calculator{
    font-family: Arial, Helvetica, sans-serif;
    background-color: hsl(0, 0%, 20%);
    border-radius: 15px;
    width: 320px;
    overflow: hidden;
}

#display{
    width: 100%;
    height: 100px;
    font-size: 3rem;
    text-align: right;
    border: none;
    padding-right: 15px;
    background-color: hsl(0, 0%, 9%);
    color: white;
}

#display::placeholder{
    color: rgb(255, 102, 0);
}

#keys{
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    padding: 15px;
}

button{
    height: 70px;
    border-radius: 50%;
    border: none;
    background-color: hsl(0, 0%, 20%);
    color: white;
    font-size: 1.5rem;
    font-weight: bold;
    cursor: pointer;
}