style.css

*{
    margin: 0;
    padding: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}

:root{
    --body-color: #2c2c2c;
    --text-color: #fff;
}

body{
    background: var(--body-color);
    color: var(--text-color);
    overflow: hidden;
    transition: 500ms all;
}

body.light{
    background: rgb(255, 255, 255);
    color: #2c2c2c;
}

main{
    display: flex;
    justify-content: center;
    align-content: center;
    align-items: center; 
    padding: 10px;
    height: 100vh;
}

main .container{
    border: 1px solid rgb(114, 114, 114);
    padding: 20px;
}

main button{
    position: absolute;
    top: 10px;
    right: 10px;
    padding: 5px;
    border-radius: 8px;
    border: none;
    cursor: pointer;
}