Add space below fixed header on mobile

On mobile my fixed nav covers the photo with text heading below it too much. How can I safely move all headings below the nav down like 150px for mobile views? I did this successfully for anchor links, but don't know what to target for all first content on all pages for a certain mobile breakpoint. The anchor link didn't require a block ID or page element to target.

Thanks.

Hi,

What is site url?