IE problems

I want to use Dropdown Menu Widget in a new widgetized theme of https://www.bootjesgek.nl (not actual yet). It works well in FF, Opera, Chrome but not in Internet Explorer.
Sublevels were hiding after the content of the site; this was solved by using a z-index:

`#menu{
padding: 0;
width: 100%;
clear: both;
z-index: 200;/*IE*/
position: relative;/*z-index*/
list-style: none;/*FF,Chrome,Opera*/
}`

Problem that I could not solve:
Sublevels of the categories appear under the next category on the right with the first sub hidden behind the knob of the main category.

https://www.ads-software.com/extend/plugins/dropdown-menu-widget/