Twenty Fifteen: Add gradient background options that fit the theme color scheme

[ianbelanger]

Now that we have the option for certain blocks to have gradient backgrounds, we need to add gradient background options to the theme that fit the themes color scheme.

Add theme support and css classes for gradient background options in the twentyfifteen theme.

I used the theme colors for "from" and lightened or darkened by 10% to get the "to" colors.

Trac ticket: https://core.trac.wordpress.org/ticket/49760

Here's a screenshot of the gradients on the buttons:

[itsamoreh]

I submitted a PR for this. I tried to match the theme's color scheme.

This is my first ticket so let me know if I did something wrong!

[pls78]

Hi! I tested the PR and it adds gradient background options that fit the theme colour scheme.

However, I'm experiencing the same behaviour reported in this comment: https://core.trac.wordpress.org/ticket/49761#comment:4 related to twenty fourteen theme.

[pls78]

Gradient background colors before applying PR

[pls78]

Gradient background colors after applying PR

[audrasjb]

Moving for 6.0 consideration

[audrasjb]

Self assigning for review

Trac ticket: https://core.trac.wordpress.org/ticket/49760

[audrasjb]

The patch looks good to me. I put it together in a PR to run unit tests but it looks good to go, thank for testing :)

[audrasjb]

In 52722:

Twenty Fifteen: Add gradient background options using the theme color scheme.

This change implements gradient background options that fit the color scheme used in Twenty Fifteen.

Props ianbelanger, itsamoreh, pls78, audrasjb.
Fixes #49760.

[audrasjb]

Reopening this ticket because the above commit was reverted, since it was accidentally committed to branch 5.9 instead of trunk…

[audrasjb]

In 52724:

Twenty Fifteen: Add gradient background options using the theme color scheme.

This change implements gradient background options that fit the color scheme used in Twenty Fifteen.

Props ianbelanger, itsamoreh, pls78, audrasjb.
Fixes #49760.

Committed in https://core.trac.wordpress.org/changeset/52724

Committed in https://core.trac.wordpress.org/changeset/52724