Css is lost in postback

Question

I am currently having a problem with my site in ASP.net/C#. I am building a page where several elements depend on others. On this page, I use some CSS CSS classes, although they seem to get lost when Postback happens. Can someone take a look at the code and tell me where this is happening?

I used the .NET script file to insert the code for my .ascx and .ascx.cs file. Hope this will be somewhat clear. Sorry if not.

https://dotnetfiddle.net/NLwtiN

EDIT: I tried to compare the html from 2 DropDownLists, hoping there would be some significant difference, although there is no next to it