Optimize Web Page Template and Make Browser Compatible (including IE 8 as much as possible)

I have a single web page, built by another freelancer, that represents the template for a web application. It works *mostly* correctly in the latest version of IE/Chrome/Opera/Firefox. It's broken in Edge. I haven't yet tested on mobile browsers or anything like Safari or Silk, yet. I need this page to work on all modern browsers and have good legacy support for older browsers (including IE 8). The code should be simplified where possible. The CSS should be organized better for maintenance purposes. Needed Fixes: 1) I'm not convinced the burger submenu works properly (it certainly doesn't seem to have the ability to have sub-categories). 2) The sub-categories on the submenu should have a more distinctive and consistent background color and height. 3) The super-menu should have a maximum height of 3x the main menu, and the text should stop growing at that point, as well. The super-menu should have a minimum height equal to the main menu and the text should stop shrinking at that point, as well. 4) When the window is shrunk horizontally far enough, the logo gets cut off on the right and left edges. Any other anomalies found through testing. I need someone who is quick and responsive.