[Doc] Update visibility of the search button

[peytondmurray]

Why are these changes needed?

After #42313 was merged, the contrast of the search button in dark mode is too low. After a discussion in #43566, we are reverting to the default pydata-sphinx-theme style for the search button.

Related issue number

Closes #43566.

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[can-anyscale]

do you post the screenshot of the button before and after, thankks

[peytondmurray]

Before

After

cc @simran-2797

[simran-2797]

Awesome! Lgtm.
Qq: The search behavior still remains the same, right? I click on the search bar and I would see this?

[peytondmurray]

@simran-2797 It should be, is the test deployment here behaving differently for you?

[simran-2797]

Nope. Lgtm. Thanks!

[angelinalg]

lgtm

[peytondmurray]

@can-anyscale Build failure looks unrelated, something about a failure to fetch a mirrorlist when running wanda. Can you double check? I think this should be fine to merge.