Revision diff colors aren't varied enough

[ethitter]

In 3.5, there were two colors for both additions and deletions: one for the background of a modified line, and another for individual changes with in a line. In beta, we've lost the second color for individual changes.

As a result, if a single word is added or removed, the entire line it appears in looks to be either inserted or deleted because the ins and del tags' background colors match that of the rest of the line.

Attached screenshots illustrate the issue.

[SergeyBiryukov]

Related: #23810

[ethitter]

Restores colors used for individual changes in 3.5

[ethitter]

At the very least, we should restore the background colors used in 3.5 for the ins and del elements. ​24038.patch does that.

The accessibility group should weigh in on the possible use of patterns or other indicators to differentiate between the line and word changes.

[bpetty]

Agreed, this should just go in now. I'm still not sure if anything is going to happen with #23810 before release (everyone seems pretty busy/backlogged with post formats).

[ocean90]

Duplicate of #23810.