The menu div sits inside a container div which has a width of 100% and a max-width set to whatever width you want the menu to be.
The menu div has a black background so that you can see the layout more clearly as you add list items. Set it to “none” when you are done.
Look at the relative positioning of the menu, ul and li to see how the menu is centered.
The rest of the content is used to fill up the page and make it look more interesting!
The static background image uses jQuery and backstretch.js. The photo is taken on the Scottish Isle of Sky from the Sleat Penninsul looking across Loch Eishort to the Cuillins.
Once you have completed the menu you will have enough confidence & technical ability to get to Mars...
It looks relatively easy to get there - probably a lot easier than creating hacks to get a website to work on Internet Explorer. Maybe someday soon Microsoft will decide to move to another planet and we can all have simpler lives!