fix(theme-classic): make focused link outlined with JS disabled

[Josh-Cena]

Motivation

Fix partially #6411. A better fix would be to use :focus-visible where available and only fall back to using JS when the former is not available, but can't be bothered now.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Turn off JS and use tabs to navigate the page. Compare the behavior to the prod website.

[netlify]

✔️ [V2]

🔨 Explore the source changes: 3643aaf

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/61f4f6ff027b870007aa404d

😎 Browse the preview: https://deploy-preview-6505--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	72
🟢 Accessibility	100
🟢 Best practices	93
🟢 SEO	100
🟢 PWA	92

Lighthouse ran on https://deploy-preview-6505--docusaurus-2.netlify.app/

[github-actions]

Size Change: +103 B (0%)

Total Size: 755 kB

Filename	Size	Change
website/build/assets/js/main.********.js	573 kB	+70 B (0%)
website/build/index.html	30.1 kB	+33 B (0%)

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	47 kB
website/build/assets/css/styles.********.css	105 kB

_{compressed-size-action}

[slorber]

LGTM 👍