General styling: remove long-content-fade SCSS mixin and use the one exported by @wordpress/base-styles

[zaguiini]

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.

[vykes-mac]

created a PR WordPress/gutenberg#46485. Seems I can't add labels as a first time contributer

[p-jackson]

w.r.t WordPress/gutenberg#46485 see p1671421937566529-slack-C0347E545HR

Is it really necessary to change our upstream dependency? What's the harm of importing a bunch of SCSS mixins if they don't get used? If there are naming collisions perhaps it'd be better for us to change our names to avoid confusion with the GB mixins anyway.

[zaguiini]

Are we going to work on this? 👀

[vykes-mac]

I looked at this and the change that is required for this simple thing has gotten huge. I don't think the effort is worth the results.

[autumnfjeld]

Should this be closed? Or moved into the backlog?

[vykes-mac]

Yup I intended to close it