Nail is not a css or html term, it's the metal thing you hammer into 2 planks to hold them together.
You were not validating for other reasons, if you don't put the span within the tags it won't have the hover element, so obviously your gallery won't work.
This is how you should write your li tags
></pre>
<li>
?????
???? ??? ??? ???? ????? ???????
Note that the class which you had on the
tag is now on the tag, and you were missing alt tags for all your images which will prevent validation.
Now to the positioning of your photo gallery. As I said in the previous post
If you make all your hover images the same size you do not need to give them an id, they will appear in the same place from any of the nav links.