Fixes

Fixes #4829 by @fcoveram

Description

This PR updates the skeleton colors to match the updated designs.

It also fixes the number of columns when the sidebar is visible: the isSidebarVisible prop wasn't passed, so the number of columns was set the same when the sidebar was open, and the screen was narrower, as when it was closed.

It also moves some styles to Tailwind classes, and simplifies the Storybook story.

Testing Instructions

Open the browser devtools and set slower speed in the "Network" tab's throttling settings.
Try searching for something in Openverse. Use some new search terms to prevent loading from cache. You should see loading skeletons. The number of columns in "All content" view should match the number of columns in the results when the filters sidebar is open (In staging, you can see that there are more columns of the skeleton than of the search results when the sidebar is open)

Check the loading skeletons in Storybook, in both dark and light modes.
Emulate prefers reduced motion using the browser devtools, and see that the skeletons are not animated.

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• I ran the DAG documentation generator (ov just catalog/generate-docs for catalog
  PRs) or the media properties generator (ov just catalog/generate-docs media-props
  for the catalog or ov just api/generate-docs for the API) where applicable.

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