style.css

* {
    margin: 0px;
    padding: 0px;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
}

body {
    background-image: linear-gradient(to right, turquoise, rgb(80, 184, 106));
    height: 100vh;
    width: 100vw;
}

header h1 {
    color: white;
    margin: auto;
    padding: 30px;
    text-align: center;
}

main {
    height: 60vh;
    width: 60vh;
    background-color: rgb(22, 16, 54);
    border-radius: 20px;
    margin: auto;
    display: grid;
    grid-template-columns: repeat(3, auto);
    justify-content: center;
    justify-items: center;
    align-content: center;
    align-items: center;
}

.cell {
    width: 20vh;
    height: 20vh;
    border-radius: 5px;
    display: flex;
    border: 5px, solid, rgb(249, 248, 250);
    /*background-color: grey;*/
    line-height: 20vh;
    color: white;
    text-align: center;
    justify-content: center;
    justify-items: center;
}

.cell:hover {
    background-color: rgba(255, 255, 255, 0.1);
}

.output input:hover {
    background-color: rgb(49, 45, 66);
}

.output {
    text-align: center;
    color: white;
    padding-top: 30px;
}

.output input {
    width: 200px;
    height: 75px;
    background-color: rgb(22, 16, 54);
    color: white;
    border-radius: 10px;
    margin-top: 20px;
}

footer {
    margin: auto; 
    color: white;
    text-align: center;
    margin: 30px;
}

footer a {
    text-decoration: none;
    font-weight: bold;
}