Merge pull request #16592 from edx/fix-footer-scope-to-fix-btn-styling

Scope base build to footer only.

lms/static/sass/_build-footer-edx.scss

 // ----------------------------------------
 // LMS edx.org Footer: Shared Build Compile
-
-// Base build
-@import 'base/build';
+@import 'lms/theme/variables';
+@import 'bootstrap/variables';
+@import 'bootstrap/scss/variables';
+@import 'bootstrap/scss/mixins/breakpoints';
+@import '../variables';
+@import 'lms/theme/variables-v1';
+@import 'base/mixins';
 
 footer#footer-edx-v3 {
   @import 'base/extends';
-
-  // base - starter
   @import 'base/base';
 }
 
-// base - elements
 @import 'elements/typography';
-
-// shared - platform
 @import 'shared/footer-edx';
-
-// Extra theme-specific rules
 @import 'lms/theme/extras';