---

效果图

---

---

html+css

html

<div class="s">
    <input type="checkbox" id="si" class="si">
    <label for="si" class="sl"></label>
</div>

---

style

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

body {
    background-color: rgb(255, 68, 68);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
}

.s {
    width: 80px;
}

.si {
    display: none;
}

.sl {
    display: block;
    width: 80px;
    height: 40px;
    border: 2px solid #cccccc;
    border-radius: 20px;
    padding: 2px;
}

.sl::after {
    display: block;
    content: '';
    width: 50%;
    height: 100%;
    position: relative;
    left: 0;
    background-color: #acacac;
    border-radius: 50%;
    transition: all .5s ease-in;
}

.si:checked+.sl::after {
    left: 50%;
}

body:has(.si:checked) {
    background-color: rgb(68, 68, 255);
}

---

html+css+JS

html

<div class="s">
    <input type="checkbox" id="si" class="si" onclick="handleSwitch(this)">
    <label for="si" class="sl"></label>
</div>

---

style

:root {
    --bc: rgb(255, 68, 68);
}

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

body {
    background-color: var(--bc);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
}

.s {
    width: 80px;
}

.si {
    display: none;
}

.sl {
    display: block;
    width: 80px;
    height: 40px;
    border: 2px solid #cccccc;
    border-radius: 20px;
    padding: 2px;
}

.sl::after {
    display: block;
    content: '';
    width: 50%;
    height: 100%;
    position: relative;
    left: 0;
    background-color: #acacac;
    border-radius: 50%;
    transition: all .5s ease-in;
}

.si:checked+.sl::after {
    left: 50%;
}

---

function handleSwitch(event) {
    let body = document.querySelector('body');

    if (event.checked) {
        body.style.setProperty('--bc', 'rgb(68, 68, 255)');
    } else {
        body.style.setProperty('--bc', 'rgb(255, 68, 68)');
    }
}