Accessibility updates - main landmark roles (#17106)

* Removed multiple main tags from home page

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Removed multiple occurances of main in case-studies page

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Replaced css for main tag with .main-section class

Signed-off-by: ChaitanyaKaranam <karanam.krishna.25@gmail.com>

* Added main landmark role for all the pages

Signed-off-by: ChaitanyaKaranam <karanam.krishna.25@gmail.com>

* Force checks.

request-checks: true

assets/sass/_size.sass

@@ -26,7 +26,7 @@ section, header, #vendorStrip
   padding-left: $full-width-paddingX
   padding-right: $full-width-paddingX
 
-  main
+  .main-section
     width: $main-width
     max-width: $main-max-width
 
@@ -59,7 +59,7 @@ header
   .nav-box + .nav-box
     margin-left: $nav-box-sibling-margin-left
 
-  main + main
+  .main-secton + .main-section
     margin-top: $main-nav-main-sibling-margin-top
 
   .left .button