You can add custom HTML to appear above every forum page. For example, you might want to provide links or a logo. Keep in mind that any images have to be hosted on a site that you provide, as there is no means to upload it into POP Forums. Also keep in mind that POP Forums will strip out any
iframe tags, so they don't interfere with the operation of the forum or introduce a vulnerability. You can however take advnatage of Bootstrap styling and menus, since they're already loaded into the forum.
To insert custom HTML:
POP Forums does not support debugging your custom HTML. It's up to you (and your designers and code gurus) to get the look right.