Twenty Nineteen: Improve compatibility with custom colors in the separator block.

[kjellr]

There's a new Gutenberg feature that adds custom color support to the separator block:

​https://github.com/WordPress/gutenberg/pull/16784

The custom color functionality added in that ticket is incompatible with Twenty Nineteen. The theme's styles override the custom colors in a couple places, and result in a mismatch between the front end and the editor. I'm attaching a small patch to fix that.

The separator color functionality is set for the 6.3 release of Gutenberg, so this should be fixed in Twenty Nineteen before that version is merged in, in order to ensure that the theme works with that functionality at launch.

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To test:

• Run a development version of Gutenberg with master active (or, wait until Gutenberg 6.3 is available in plugin form, and test with that)
• Start a post with all three styles of the separator block. Ensure that by default, these appear as intended in the editor and in the front end.
• Using the new sidebar controls, assign a color to each of the separators, and ensure that the new color shows up in the editor and in the front end.

---

Before

Editor

Front End

After

Editor

Front End

[SergeyBiryukov]

In 45920:

Twenty Nineteen: Improve compatibility with custom colors in the separator block.

Props kjellr.
Fixes #47811.