Fix logo color on error page layout

[krysal]

Fixes

Fixes #751 by @krysal

Description

Small PR to change the link color for the Openverse logo in the error page layout.

Checklist

• My pull request has a descriptive title (not a vague title like Update 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.

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[zackkrida]

LGTM