Here is how I would fix this:

1. Right click on the broken thing and go to "inspect" or "inspect element" depending on your browser.

2. This will open up a bunch of information about the page, you should make your browser window very wide so you can see everything

3. The box of broken buttons is in a <ul> </ul> html element, shown in the inspector. If we click this ul thing (which might already be selected because it's the thing we did 'inspect' on), it shows the CSS for that ul element below it in the inspector. In this particular instance, the CSS for that box of buttons is called ".side .md ul:first-child" as you should be able to see in the inspector.

4. The fact it's overlapping other stuff shows it's a positioning issue. Within ".side .md ul:first-child { }" we can see that there is the CSS property "position: absolute;"

5. Uncheck or delete this property in the inspector, and we can see that the bar of buttons jumps to the right spot. So this means instead of "position: absolute;" we instead want "position: unset;" and it would work properly

6. Now open your sub CSS and find an entry that corresponds to ".side .md ul:first-child" and find within that where it says "position: absolute;" and change this to "position: unset;"

7. Save your CSS and your sub's CSS should be fixed!

Hopefully that helps, and will give you the tools to diagnose and correct future CSS problems. Let me know if you have any questions.