style.css

@import url('https://fonts.googleapis.com/css2?family=Berkshire+Swash&display=swap');

:root {
    --light-theme: linear-gradient(#2980B9, #6DD5FA, #FFFFFF);
    --dark-theme: linear-gradient(#2c3e50 10%, #000 74%);
}

body {
    background: var(--light-theme);
    overflow: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    flex-direction: column;
    gap: 2rem;
    font-family: 'Berkshire Swash', cursive;
    font-size: 2em;
    text-shadow: 5px 5px 2px #2980B9;
    transition: .5s linear;
}

body.dark {
    background: var(--dark-theme);
    text-shadow: 5px 5px 2px #2c3e50;
    color: #fff;
    background-attachment: fixed;
    transition: .5s linear;
}

.checkbox {
    opacity: 0;
    position: absolute;
}

.label {
    width: 90px;
    height: 30px;
    background: var(--light-theme);
    display: flex;
    border-radius: 50px;
    align-items: center;
    justify-content: space-between;
    padding: 5px;
    position: relative;
    transform: scale(1.5);
    cursor: pointer;
}

.ball {
    width: 30px;
    height: 30px;
    background-color: white;
    position: absolute;
    top: 5px;
    left: 4px;
    border-radius: 50%;
    transition: transform 0.2s linear;
}

.moon,
.sun {
    height: 25px;
    margin: 2px;
}

.label.dark {
    background: var(--dark-theme);
}

.checkbox:checked+.label .ball {
    transform: translateX(60px);
}