Permanent style css change with cookies light and dark theme with javascript

Question

Hi id like that the color of the theme remains permanet when user go to another page, or when users left the web site and then return. I think that the way is with cookies, but i dont know how to do, thanks.

function swapStyleSheet(sheet){
    document.getElementById('pagestyle').setAttribute('href', sheet);
}

<p class="copyright theme">
    <a onclick="swapStyleSheet('css/dark.css')" href="#">Dark theme</a> 
    <a onclick="swapStyleSheet('css/style.css')" href="#">Light theme</a>
</p>

How i can implement with local storage?