Add context for navigation states
added find course to dashboard sidebar and included check for context that Will adds in PR
removed nav_course_search context due to design change so replaced with nav_hidden
Removed rwd_header.js and all references as no longer being used.
Wrapped Find Courses in dashboard sidebar in if statement
* adds in Sass placeholder to mirror older/inherited button styling used in LMS
* uses light theming Sass variables for button styling
* adds specific selector for certificate download button
- Doubled up :hover and :focus styling to improve a11y
- Increase contrast of certain UI elements for improved a11y
- Added some image alt text for a11y
- Changed video caption styling to blue and made them underline on hover and added a skip link before video for screenreaders.
Fixes Bugs:
- LMS-1336
