[website] Fine-tune button styles on the branding theme

[zanivan]

• I have followed (at least) the PR section of the contributing guide.

This PR is to add some components to experiments gallery and branding theme, and to tweak buttons styles.

Changes include:

• Fine-tune border radius of button variants to be consistent, and closer to shape.borderRadius in all sizes.
• Further tweak the button styles, to be more consistent among themselves.
• Add active states to buttons.
• Add <Card variant="elevation"/> to brandingTheme

Preview:

👉 https://deploy-preview-43082--material-ui.netlify.app/experiments/website/branding-theme-test/

[mui-bot]

Netlify deploy preview

https://deploy-preview-43082--material-ui.netlify.app/

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[aarongarciah]

Looks good.

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Probably unrelated to this PR, but this label is off:

[zanivan]

Probably unrelated to this PR, but this label is off:

Yep, I'm aware, and it's really bad tbh—I'll open another PR specifically for tweaking textfields. I didn't change anything related to this one yet, just added to the components' gallery. We're using many different TexFields among the website, and most of the styles are locally, so I thought it would be good to have a PR specific for them 😅