Custom CSS behaving differently depending on browser

I posted 4 weeks ago on aligning different sections of my website that is in development at https://www.logicomm.us/Sandbox/CM/SBX4/, and had a lot of great help from Dave Bardell (@rdellconsulting). I have since figured out how to load a background image in my content wrapper the way my client wants it, but now I find that some of my prior work is all out of whack, especially when viewed in Chrome (v. 40.0.2214.111 m) and Firefox (v.35.0.1), but the centering of the menu and closing up the spacing between the menu and slider look fine in Safari, v. 5.1.7 (I use a PC).

I have cleared all my caches, tried reloading the code snippets I got originally, and am really frustrated why it suddenly doesn’t work!

I need to adjust the width of the logo in the header, the slider and the body so that they all align and still need help on that. However, until I can figure out why the custom CSS I had isn’t working, I am kind of stuck! Help! Help!