[DS-1076] Fix heading position for pages without alerts banner for mobile screens

[aleevas]

DS-1076

Steps to test:

• Log in as admin https://sandbox-carnation-std-virtual-y.y.org/
• Create a Landing page Layout Builder
• Add Virtual Y Content block in LB and save the page
• switch to mobile screen
• As an anonymous user log in to the site, then open the created page scrolls down

Quality checks:

Please check these boxes to confirm this PR covers the following cases:

• Maintaining our upgrade path is essential. Check one or the other:
  • This PR provides updates via hook_update_N or other means.
  • No updates are necessary for this change.
• Front end fixes should be tested against all of the Open Y Themes.
  • Tested against Carnation
  • Tested against Lily
  • Tested against Rose
  • This change does not contain front-end fixes.
• I have flagged this PR "Needs Review" or pinged the VY devs/QA
  team in Slack