style.css

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body{
    background: #2b2b2b;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    min-height: 100vh;
    transition: 0.5s;
}

body.active{
    background: #f8f8ff;
}

#toggle{
    position: relative;
    display: block;
    width: 320px;
    height: 160px;
    border-radius: 160px;
    background: #222;
    transition: 0.5s;
    box-shadow: inset 0 8px 60px rgba(0, 0, 0, 0.1), inset 0 8px 8px rgba(0, 0, 0, 0.1),
    inset 0 -4px 4px rgba(0, 0, 0, 0.1);
}

#toggle > .indicator{
    position: absolute;
    top: 0;
    left: 0;
    width: 160px;
    height: 160px;
    border-radius: 50%;
    background: linear-gradient(to bottom, #444, #222);
    cursor: pointer;
    transform: scale(0.9);
    transition: 0.5s;
    box-shadow: 0 8px 40px rgba(0, 0, 0, 0.5), inset 0 4px 4px rgba(255, 255, 255, 0.2), 
    inset 0 -4px 4px rgba(255, 255, 255, 0.2);
}

#toggle.active{
    background: #f8f8ff;
    box-shadow: inset 0 2px 60px rgba(0, 0, 0, 0.1), inset 0 2px 8px rgba(0, 0, 0, 0.1),
    inset 0 -4px 8px rgba(0, 0, 0, 0.05);
}

#toggle.active > .indicator{
    left: 160px;
    transition: 0.5s;
    background: linear-gradient(to bottom, #e5e4e2, #fff);
    box-shadow: 0 8px 20px  rgba(0, 0, 0, 0.1), inset 0 4px 4px rgba(255, 255, 255, 1),
    inset 0 -4px 4px rgba(255, 255, 255, 1);
}