CSS Theme Change
Change CSS theme with toggle, buttons or select using CSS properties
...It can react to user toggles as well as automatically adapt to the user’s OS-level dark/light mode settings, helping developers build interfaces that feel modern and responsive without writing boilerplate theme code. Because it abstracts away cross-browser quirks and standardizes how CSS variables or classes are applied, it saves time and reduces bugs related to inconsistent theme behavior. It’s also modular and tiny in size, meaning it can be dropped into static sites, component libraries, or SPAs without significantly increasing bundle size.