Updating npm dependencies and getting the build to work (#1001)

* Updating npm dependencies and getting the build to work

* update node in github actions to 14.x

theme/theme.config

@@ -17,6 +17,8 @@
    specify theme name below
 */
 
+@placeholder: 'default';
+
 /* Global */
 @site       : 'pxt';
 @reset      : 'default';
@@ -87,7 +89,7 @@
          Import Theme
 *******************************/
 
-@import "theme.less";
+@import (multiple) "theme.less";
 
 @fontPath  : 'fonts';