Details

We're defining our own version of the long-content-fade mixin and it's pretty much a copy-paste of what we have in @wordpress/base-styles.

It's a good idea to remove our version and use the one shipped by the agnostic package. That way, we'd have a single source of truth and something that the community maintains, essentially one less point of maintenance for us.

Checklist

• In @wordpress/base-styles, extract the long-content-fade mixin to its own file so we can import it exclusively
• Remove the version from Calypso and import the long-content-fade file inside client/assets/stylesheets/shared/mixins/_mixins.scss
• Check that all usages of long-content-fade did not introduce regressions, including the places where we're not defining the $color variable, which has a different default value in the mixin definition

Related

#65598.