remove unnecessary parentheses

change css properties for mixins bi-aap in login/register page

change css properties for mixins bi-app in about course page

change css properties for mixins bi-app in the dashboard

change css properties for mixins bi-app in help template

change css properties for mixins bi-app in the home page

change css properties for mixins bi-app in jobs, press and media pages

remove the extra spaces

SASS compilation variable conventions update, focusing on basic colors, baseline variable usage for padding and margins, ui-depth extends, along with other small fixes. The intent with this is to not have any user-facing impact, and instead move us closer toward having files that use our newer sass conventions.

- 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