Fix WordPress Mobile and Tablet Responsivness

I recently added a few custom components to my WordPress site and, while most of the desktop work looks okay, the responsive behaviour needs help. On both smartphones and tablets the main navigation either appear badly, renders half-off screen, or breaks its layout altogether... (Budget: $30 - $250 CAD, Jobs: CSS, Frontend Development, HTML, JavaScript, PHP, UI / User Interface, Web Development, WordPress)