style.css

.container {
    max-width: 1000px;
    margin: auto auto auto auto;
    border-radius: 15px;
}

#display {
    text-align: right;
    height: 70px;
    line-height: 70px;
    padding: 16px 8px;
    font-size: 25px;
    background-color: rgb(255, 255, 255);
    border-radius: 15px;
    margin-bottom: 10px;
}

.buttons {
    display: grid;
    grid-template-columns: 1fr 1fr 1fr 1fr;
    color: white;
    font: bold;

}

body {
    background-color: black;

}

h1 {
    text-align: center;
    font: bold;
    font-family:'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
    color: white;

}

.buttons>div {
    border-top: 1px solid #999;
    border-right: 1px solid#999;
}

.button {
    border: 0.5px solid #999;
    line-height: 100px;
    text-align: center;
    font-size: 25px;
    cursor: pointer;
    border-radius: 15px;
}

#equal {
    background-color: blue;
    color: white;
}

#clear {
    background-color: rgb(248, 64, 95);
    color: black;
}

.button:hover {
    background-color: rgb(173, 171, 243);
    color: white;
    transition: 0.5s ease-in-out;
}