title: Dark/Light mode using two CSS files
body: <p>I am using a web software, that allows to create themes. It creates a single CSS file per theme, so i've got two CSS files: dark.css and light.css.</p>
  
  <p>What's the best way to create a dark/light mode <strong>switch</strong> (independent from the visitor's system settings) using both CSS files? I've tried loading the opposite theme upon click, but that's very impractical and requires at least one more roundtrip.</p>
  
  <p>I can embed the CSS files contents into the DOM, if that helps to achieve a smooth switch.</p>