Update CSG_GUIStyleUtility.cs

[MrLeap]

Change the X tooltip to indicate how to close the addon, since that is the wish inside the heart of every human who first moves to click it.

[nukeandbeans]

A good start, though I feel like a change to the actual buttons would be better. E.g. a ^ button to the left of the x button, so the popout option is more obvious, and the close button actually closes it. The close button could then just have a tooltip with something like "Press CTRL+F3 to re-enable/toggle".

There are some things that'd need to be considered with the tooltip, like user keybindings and such. It'd need to update with the binding set by the user.