Fixes part of #4177: Dark mode Topic Activity Part 1

[MohitGupta121]

Explanation

Fixes part of #4177 : Dark mode Topic Activity Part 1 (Toolbar + Tabs)

Dark Mode Mockup:-
https://xd.adobe.com/view/c05e9343-60f6-4c11-84ac-c756b75b940f-950d/screen/3b067181-e5e0-4a5b-bbb8-ab5eda952549/specs/

Default	Dark Mode

Essential Checklist

• The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• Any changes to scripts/assets files have their rationale included in the PR explanation.
• The PR follows the style guide.
• The PR does not contain any unnecessary code changes from Android Studio (reference).
• The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

If your PR includes UI-related changes, then:

• Add screenshots for portrait/landscape for both a tablet & phone of the before & after UI changes
• For the screenshots above, include both English and pseudo-localized (RTL) screenshots (see RTL guide)
• Add a video showing the full UX flow with a screen reader enabled (see accessibility guide)
• Add a screenshot demonstrating that you ran affected Espresso tests locally & that they're passing

[MohitGupta121]

@rt4914 can you please review this PR for Part 1 of #4177

[rt4914]

LGTM, Thanks.

[rt4914]

@MohitGupta121 In future please make sure you use Fixes part of #xxxx in title and description as you are not finishing the entire issue in this PR. For now I have updated these.

[MohitGupta121]

@MohitGupta121 In future please make sure you use Fixes part of #xxxx in title and description as you are not finishing the entire issue in this PR. For now I have updated these.

Okay thanks you, I take care next time.