feat(theme): add mockingbird theme (@chinmaydwivedi)

[chinmaydwivedi]

Description

Checks

• [ yes] Adding quotes?
  • [yes] Make sure to include translations for the quotes in the description (or another comment) so we can verify their content.
• [ yes] Adding a language or a theme?
  • [yes] If is a language, did you edit _list.json, _groups.json and add languages.json?
  • [yes] If is a theme, did you add the theme.css?
    • Also please add a screenshot of the theme, it would be extra awesome if you do so!

<--Theme while overview--> <--Color flip Mode--> <--Color full Mode--> - [none] Check if any open issues are related to this PR; if so, be sure to tag them below. - [yes] Make sure the PR title follows the Conventional Commits standard. (https://www.conventionalcommits.org for more info) - [okay] Make sure to include your GitHub username prefixed with @ inside parentheses at the end of the PR title.

Closes #

[FFUV]

please show example pictures!

[Miodec]

Screenshots missing

[chinmaydwivedi]

Screenshots missing

please show example pictures!

sorry i forgot to do that earlier, I just updated the description.

[FFUV]

beautiful theme honestly

[FFUV]

Bump merge this

[Miodec]

Sorry, look like a duplicate of paper, with worse color choices. For example here it looks like these buttons are on, but they are in fact off.

[FFUV]

Sorry, look like a duplicate of paper, with worse color choices. For example here it looks like these buttons are on, but they are in fact off.

looks like but is it really?