Сергей Ракипов,
вариант со сменой класса ...
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style>
html.bg1 body{background-color: hsla(0, 100%, 60%, 1)}
html.bg2 body{background-color: hsla(150, 50%, 40%, 1)}
html.bg3 body{background-color: hsla(252, 100%, 50%, 1)}
</style>
<script>
(function() {
var html = document.querySelector('html')
var x = localStorage.x || 1;
html.classList.add(`bg${x}`);
})()
</script>
</head>
<body>
<div class="bg-image "></div>
<select class="bg" size="1" onchange="6">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<script>
document.addEventListener( "DOMContentLoaded" , function() {
document.querySelector('.bg').value = localStorage.x || 1;
document.querySelector('.bg').addEventListener("change", function() {
localStorage.x = this.value;
window.location.reload()
})
});
</script>
</body>
</html>