style.css

:root {
	--label: #111;
}

html, body {
    margin: 0;
    padding: 0;
    height: 100%;
    width: 100%;
}

.toggle {
    display: none;
}

.toggle + label {
    width: 42px; 
    height: 20px;
    background: var(--label); 
    display: block;
    position: relative;
    border-radius: 30px;
    padding: 2px;
    transition: 200ms;
    cursor: pointer;
    background-image: url(./assets/sun.png);
    background-position: right center;
    background-repeat: no-repeat;
    background-size: 20px;
    background-position-x: 24px;
}

.toggle + label:before {
    content: '';
    position: absolute;
    height: 20px;
    width: 20px;
    background: white;
    display: block;
    border-radius: 50%;
    right: unset;
    left: 2px;
    top: 2px;
    transition: 200ms;
}

.toggle:checked + label {
    background-image: url(./assets/moon.png);
    background-repeat: no-repeat;
    background-position: left center;
    background-size: 20px;
    background-position-x: 2px;
}

.toggle:checked + label:before {
    content: '';
    left: calc(100% - 22px);
    box-shadow: 0 4px 4px rgb(0 0 0 / 10%);
} 

.theme-light {
    --color-primary: #0060df;
    --color-secondary: #fbfbfe;
    --font-color: #000000;
}

.theme-dark {
    --color-primary: #17ed90;
    --color-secondary: #243133;
    --font-color: #ffffff;
}

.container {
    display: flex;
    width: 100%;
    height: 100%;
    background: var(--color-secondary);
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

.container p {
    color: var(--font-color);
    text-align: center;
}