[SPARK-46863][DOCS] Cleanup custom CSS

[nchammas]

What changes were proposed in this pull request?

• Remove rules for the following classes that we do not use:
  • .code (We use code elements, but not a code class.)
  • .code-tab (We do have a codetabs class, however.)
  • .jumbotron (No idea where this came from, but we don't use it.)
• Remove some superfluous comments.
• Using css-purge, merge rules for the same selectors that were previously scattered across several blocks, and remove overridden rules.
• Format the whole file with VS Code. This makes the spacing consistent, and puts each selector on its own line.

Why are the changes needed?

It's very difficult to make improvements to the presentation of the documentation due to the noise in this CSS file. This change will facilitate future improvements to the documentation.

Does this PR introduce any user-facing change?

No, it shouldn't. This change should be functionally neutral.

How was this patch tested?

I built the docs and manually reviewed them. Code blocks and tables look the same to me.

Was this patch authored or co-authored using generative AI tooling?

No.

[nchammas]

cc @gengliangwang and @grundprinzip.

I am trying to fix how code and text inside tables wrap, but I found it very difficult to do due to a few problems in custom.css. This PR makes an initial round of cleanup.

In a future PR, I intend to reduce our use of the .global class selector, which is very invasive due to its specificity, and makes it harder to define simple styling rules for tables.

[yaooqinn]

Thanks, merged to master