Is it possible these variables already stopped working in Bootstrap 5.3.0?
We used these variables to make the background and border for alert a bit lighter so they are a bit more subtle and the text is better readable (higher contrast). But since Bootstrap 5.3.0 this no longer works. Any value we set seems to be ignored.

Is there a recommended alternative for this?

Hi @kreintjes

Please note for your next questions that the GitHub Discussions > Q&A is more appropriate. Having questions in already merged PRs or closed issues is difficult to track for us :)

Back to your question, $alert-bg-scale, $alert-border-scale, and $alert-color-scale have been deprecated in v5.3.0 with the apparition of the dark mode (they don't do anything from v5.3.0) and will be removed entirely in v6.

Before we did the following:

@each $state, $value in $theme-colors {
  $alert-background: shift-color($value, $alert-bg-scale);
  $alert-border: shift-color($value, $alert-border-scale);
  $alert-color: shift-color($value, $alert-color-scale);
  /* etc. */
}

The dark mode doesn't permit keeping this solution so it's now defined as

If you'd like to keep the previous system, you'll need to override the rules in your project.