Merge branch 'eduardosanz/background-file-holder' into 'master'

Remove $white color to improve dark mode

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145590



Merged-by: Payton Burdette <pburdette@gitlab.com>
Approved-by: Jay Montal <jmontal@gitlab.com>
Approved-by: Payton Burdette <pburdette@gitlab.com>
Approved-by: Sascha Eggenberger <seggenberger@gitlab.com>
Co-authored-by: Eduardo Sanz García <esanz-garcia@gitlab.com>