Top-level pages have issues on mobile

[chalin]

There are formatting issues with the vendor page on mobile. Here's a screenshot:

Issues:

• Notice the white bar between the top nav and the blocks/lead, this bar should be removed:
  • Vendor page: use blocks shortcode and markdown instead of (invalid) HTML #1171
  • Registry page: use blocks shortcode and markdown instead of (invalid) HTML #1174
  • Status page: use blocks shortcode and markdown instead of (invalid) HTML #1175
  • Integrations page: use blocks shortcode and markdown instead of (invalid) HTML #1176
• Use a single file rather than a section to generate the page:
  • Vendors: use single file, not a section; and other cleanup #1173
  • Registry page: use blocks shortcode and markdown instead of (invalid) HTML #1174
  • Status page: use blocks shortcode and markdown instead of (invalid) HTML #1175
  • Integrations page: use blocks shortcode and markdown instead of (invalid) HTML #1176
• Vendor-page specific
  • Vendors: use single file, not a section; and other cleanup #1173
  • For remaining items, see Vendor page: improve vendor list presentation on mobile #1196

[chalin]

All done. For remaining items, see #1196.