Hmmm? CSS/WordPress newbie’s CSS positioning dilemma. Just 1 error….

(Hm, I tried posting this request two times prior, but it simply does NOT show up in the posts, and something’s definitely wonky about my profile and the controls, everything is blank…. anyway…update, i found out the reason why they were disappearing, they were flagged as spam since I pasted three codes, I thought it was more polite the paste the code than just force the reader to search off on his own, hehe..)

I really appreciate the generous time you donate to helping me out with this problem.
I’m new to wordpress and CSS, know HTML.

I installed a new theme, but problem:

1. on the main index page, the Menu Div’s positioning is haywire, and suddenly is on TOP of my blog entries (yep, VERY VERY ugly)
2. but if you click “about” link, or other various links, the Menu Div is properly to the right of the blog entries.
3. The strange Menu Div positioning problem appears hence, to only be on the index.php page.

visual example:
Click

What I attempted to do:

Because the problem occurred only in the index.php page, where the blog entries are, I assumed the problem was in the coding in the index page. The theme originally, appears to have VERY shoddily-written CSS, but I can’t detect anything wrong with it b/c I don’t know anything about float/positioning/box, whatever issues that I’m making a wild guess would be the root of the problem. No matter how hard I look at the index.php I cannot seem to find the error in div positioning. (I’m assuming that’s what the problem is)

but the Menu Div is FINE here:
click, fine here…

So I looked at the source code of the index.php and don’t know where the problem is.

This is where I turn to you, reader. If you could explain to me why this happened, and what coding would be needed to replace it, I would be VERY grateful ??

And if you were right here next to me, I truly would offer you a slice of crispy apple pie, hehehehe!

css code:
https://wordpress.pastebin.ca/968053

index.php’s source code:
https://wordpress.pastebin.ca/968055

and finally, code of the about page, which appears normal:
https://wordpress.pastebin.ca/968063