Now what’s quite impressive is that it does things, I didn’t order it to do, neither in the HTML nor CSS. For example, if you click on the link to Page1 it changes the logo.
Now what’s quite weird is that these are in total 6 identical HTML files, using 1 CSS file.
Did you solve this already?
I would check , not the HTML, but the CASCADE of the CSS. As you didn’t give any identifying class to the main navigation list. it is possible that other style sheets override how the LIs are displayed. merely changing li{float:left;} to li{float:right;} ( or viceversa) anywhere in the CSS would cause the problem you have just described.