How to change Expand and Collapse images of ZK Grid hierarchy Component

Today i got a new POC(Proof of concept) task how can we change the default expand and collapse images of ZK Grid hierarchy Component as i am not much knowledge of CSS i am not sure how we can do this. Its clear to me we have to make change in CSS to achieve this but in which css class i have to made the changes i am not sure then i have to ask this question Ben bai a zk developer ,very well and deep knowledge about ZK,CSS,Jquery etc. He told me to write this below CSS to achieve this



Here is the ZUL file for this ..


Note:- As i am not sure how we can get which CSS apply in which component @Ben suggest me a better way to do this in Google Chrome Browser ,What we can do is right-click on the expand/collapse icon in Chrome then click 'Inspect element' to view the dom elements and its css style in Chrome console

ZK Listbox Data Filter Demo

ZK Provide Data Filter in Listbox,Grid I have created a Very Basic Demo application to apply Filters in Listbox.
ZUL file Code
And View Model Or Java Class

Its a Very basic developer can modify the code as their requirement.