FAL-1881 Tweak header override styles to match lms header

FAL-1881

This makes the header styles closely match the lms header with the client's custom theme.

Test instructions:

Setup (ignore if testing on stage at https://discover.stage.ondemand.cloudera.com/ ):

• apply this theme to the frontend-app-course-search mfe
• update the LOGO_TRADEMARK_URL and LOGO_URL to image urls for the client (see private secure configuration vars)
• run the frontend app and navigate to the locally served url

Test:

• compare the header with that of https://stage.ondemand.cloudera.com/
• verify that the logo size and position matches
• verify that the 'courses' button styling (normal and hover) matches the lms header

Reviewers:

• @jill_opencraft