Hi Elin,
The individual list-items still have a background color, that is why your styling isn't working. The best way to solve this is to create some custom css and add it to your custom.scss file. If you are using Atlas UI 3.0, I think it should compile automatically (I haven't tried yet).
.listview-transparent.mx-listview > ul > li {
background-color: transparent;
}
And add the class to the listview you want to style:
If you don't know how to do custom styling, you can look into the Mendix learning path.
Another solution is to set the listview style to no Styling, then your solution will work as well. Upside is that this requires no custom styling, downside is you lose ALL default styling of your listview.
Hope this helps!
Cheers,
Daan