I Think I see what you are getting at. I do not know of any native way to get that done but Ive built a solution that I think does the job.
On your "X" icon set it to:
Set(Expand,false)
On your "+" icon set it to
Set(Expand,true)
Create a button with the size that you want it to be when expanded. (This will essentially be a dummy button) Lets call it Button1
Set Button1's visibility to:
If(Expand=true,true,false)
So now if you click the plus button it will show up if you click the x button it will disapear.
Now add another button thats the size you would like it to be shrunk and place it in the center Button1
Set its visibility to:
If(Expand=true,false,true)
Now you should be all set.
Here is what it will look like when clicked.
Let me know if that helps
