style.css

*{
    box-sizing: border-box;
}

body{
    margin: 0;
    background-color: rgb(211, 0, 211);
    display: flex;
    flex-direction: column;
    align-items: center;
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
    min-height: 100vh;
}

h1{
    font-size: 2.4rem;
    color: #ffffff;
}

canvas{
    background-color: #ddd;
    display: block;
    border-radius: 5px;
}

.btn{
    font-size: 1rem;
    cursor: pointer;
    padding: 8px 16px;
    border: 0;
    background-color: #000;
    color: #ffffff;
    border-radius: 6px;
}

.btn:hover{
    background-color: #222;
}

.btn:active{
    transform: scale(0.96);
}

.btn:focus{
    outline: 0;
}

.rules-btn{
    position: absolute;
    top: 30px;
    left: 24px;
}

.rules{
    position: absolute;
    top: 0;
    left: 0;
    color: #ffffff;
    background-color: #333;
    padding: 16px;
    line-height: 1.5;
    min-height: 100vh;
    width: 320px;
    transform: translateX(-320px);
    transition: transform 1s ease-in-out;
}

.rules.show{
    transform: translateX(0);
}