* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body {
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    background-color: hsl(0, 0%, 95%);
}
.calculator {
    max-width: 500px;
    font-family: Arial, Helvetica, sans-serif;
    background-color: hsl(0, 0%, 15%);
    border-radius: 15px;
    overflow: hidden;
}
.keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    padding: 20px;
}
button {
    height: 100px;
    width: 100px;
    border-radius: 50px;
    background-color: rgba(0, 0, 0, 0.553);
    font-size: 3rem;
    color: #fff;
    border: none;
    font-weight: bolder;
    cursor: pointer;
}
.display {
    width: 100%;
    border: none;
    color: white;
    text-align: left;
    padding: 20px;
    font-size: 5rem;
    background-color: hsl(0, 0%, 20%);
}
.operator {
    background-color:hsl(35, 100%, 50%);
}
.operator:hover {
    background-color:hsl(35, 100%, 65%);
}
.operator:active {
    background-color:hsl(35, 100%, 75%);
}
button:hover {
    background-color: hsl(0, 0%, 40%);
}
button:active {
    background-color: hsl(0, 0%, 50%);
}