Stop center aligning docs nav on small screen

[bobaekang]

Description

Please describe what changes you made, and why you feel they are necessary. Make sure to include
code examples, where applicable.

Docs page's nav items contain hierarchical indentation for headings that doesn't work well when text is aligned center on small screen. This PR removes the responsible text-align style to keep the nav items left-aligned on small screen. The changed style also matches the current style on larger screen.

See the following images for comparison:

Before	After

The change in this PR should not affect the style for any other part of the website since CSS .nav class is only used for the container element of docs nav items located in the www/content/docs.md file:

htmx/www/content/docs.md

Line 7 in 4a2289d

<div class="2 col nav">

Corresponding issue:

Testing

Please explain how you tested this change manually, and, if applicable, what new tests you added. If
you're making a change to just the website, you can omit this section.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded