Hi Raju,
If you really want to do this with CSS only please provide some extra details about how/where you use your widget (page structure), what data you are using and in which scenario it is not working as intended.
What type of data source are you using for the list widget?
If you are retrieving over association sorting isn't directly possible, however if you use a microflow as source and use the same association retrieve inside of that microflow, you are able to sort inside the microflow with a list operation to get your desired result.
If you use a database or Xpath source you can directly sort on the widget itself.
Hope this helps, otherwise please share some more details about your issue!
Inspect your tab and check your CSS placed on right place. And also try !important in your css.
Hope this helps.