The uploading progress bar isn't displayed anymore in light mode

I noticed that when a profile is being sent, the progress bar that used to show up at the top of the page isn't displayed anymore. According to @mstange it's still displayed in dark mode though.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-1423)

Start by reproducing a profile upload in light and dark mode, then trace the progress-bar component and its styling in the TypeScript/React frontend. Compare the two theme paths and verify that the upload progress bar is visible in light mode without regressing dark mode.

Written by the indexing model from the issue text.