Use CSS :has to set root-level styles based on a button’s state

Great tip here from Jhey. He advises using a button with ARIA and a little JavaScript for your dark-mode toggle. And to apply the dark styles, use a CSS selector which targets the :root parent of the button when in “pressed” state and sets a root-level custom property to “on”.

:root:has([aria-pressed=true]) {
  --dark:1;
}

Seriously clever stuff!

And aside from the CSS, I really like the way Jhey advocates using a button rather than a form element such as a checkbox for this kind of interface, much like Léonie did recently.