This has been in the oven for quite a while, nice to see it being enabled by default. Looks small but the implementation details are quite tricky. Hope to see it landed in other browsers. Great work by Delan and Stephen as part of Igalia collaboration with Bloomberg.

<style>
  .info { color: white; background: blue; }
  .info::selection { color: black; background: cyan; }
</style>
<div class="info">
  <strong>INFO</strong> - This is just an <em>informative</em> message.
</div>

See: https://developer.chrome.com/blog/selection-styling