refactor(v2): minor styling improvements

[lex111]

Motivation

• Fix borders of collapse doc sidebar button

• Replace e-resize type with click when hover on expand sidebar button

Before	After

• Add hover state for dark mode switcher

• Use Infima buttons on home page

Before	After

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Preview

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

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Deploy preview for docusaurus-2 ready!

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[github-actions]

Size Change: +15 B (0%)

Total Size: 156 kB

ℹ️ View Unchanged

Filename	Size	Change
website/build/assets/css/styles.********.css	17.7 kB	0 B
website/build/assets/js/main.********.js	109 kB	+14 B (0%)
website/build/blog/2017/12/14/introducing-docusaurus/index.html	21.7 kB	+1 B (0%)
website/build/docs/introduction/index.html	180 B	0 B
website/build/index.html	6.95 kB	0 B

_{compressed-size-action}

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	70
🟢 Accessibility	96
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-4167--docusaurus-2.netlify.app/classic/

[slorber]

Thanks

Was not totally satisfied with my homepage button 😅

There are some responsive problems thoughts. Also wonder if it's not better to keep the text white for dark mode?

The rest looks fine to me

[lex111]

There are some responsive problems thoughts. Also wonder if it's not better to keep the text white for dark mode?

Responsive design issues fixed, as for the color it's hard for me to make a decision - I think the default color looks good.

[slorber]

thanks, we can see later to improve if needed :)