Header color/ image, site background image
Design and Skin Customization
Looks like the issue is you've got some broken CSS in the custom styling. Not sure how that would happen. Suggest using the RESET SKIN STYLE and start again.
If you plan to make a lot of skin changes, the File System method will give you the most flexibility.
after you clone the skin:
https://www.jamroom.net/the-jamroom-network/documentation/skin-design-guide/839/creating-your-own-skin-clone-from-an-existing-skin
You can adjust the sites CSS directly from your clone skin's *.css files found via SFTP at:
/public_domain/skins/YOUR-SKIN/css/(css files are here)
Docs: "Connecting to your server using SFTP"
https://www.jamroom.net/the-jamroom-network/documentation/jamroom-hosting/2552/connecting-to-your-server-using-sftp