Hi There,
Thank you for writing in, please navigate to Theme Options > Header and set the Navbar Top Height, just enough that your content wont be covered by the header. And then remove the top paddings you applied on the content (Section 1 and sidebar).
And another thing, I notice that your Cornerstone is up to date but your X theme is left behind, please update your X theme to the latest version as well to avoid incompatibility issues.
Updating Your Themes and Plugins
Remember to clear all your caching features (plugin, server-side, CDN, and browser’s cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Hope it helps,
Cheers!