Dark mode images without javascript

Css

The <picture> element supports media query matchers and if you want to specify a different image for dark mode, you can use a different <source>. So, if there are no suitable matches or if the browser doesn’t support the <picture> element, then the default src attribute is selected.

<picture>
  <source srcset="dark.png" media="(prefers-color-scheme: dark)">
  <img src="light.png">
</picture>

If dark mode is enabled, the dark.png image will be used as the source for the img tag.