Fix styles for nested elements (link color)

[oandregal]

Backports WordPress/gutenberg#37728
Trac ticket https://core.trac.wordpress.org/ticket/55567

This fixes an issue by which link color behaves differently in the editor and front end.

Step by step reproduction instructions:

• Create a group block and set the link color to red.
• Create a paragraph block and set the link color to purple.

The expected result is that both editor and front end show the paragraph link color as purple.

[gziolo]

Committed with https://core.trac.wordpress.org/changeset/53260.