Help with dropdown navigation menu

Hi,

I’m trying to style my navigation menu, for when the screen collapses and my menu appears as a drop down menu.

I’ll post a link to the site (only just started, very basic!)

http://a16.c12.myftpupload.com/

I can’t understand it. I’m happy with it as is it full screen, but when it collapses to fit a mobile device/tablet, it appears hay-wire. The background colour changes to white, with exception for the active page, and when the cursor hovers over it. In addition to this, some of the links are centered and others are positioned to the left of the screen.

Any help would be greatly appreciated!

I’ve scowered through articles online, and tried using various code snippets, but to no avail.

Thanks in advance for your time.

Danny.