My idea is to increase the size of the Custom CSS text box.
The current text box size makes making any edits within instant apps very hard to do. A larger window would make it easier to make changes to the Custom CSS.
My current process is to copy the current Custom CSS from the instant app to a notepad, make the desired change (hoping I typed everything perfectly), then copy/paste it back into the tiny text area. Repeating the process if I want to tweak the color, or size.

Displaying the entire Custom CSS makes it much easier to read and edit

Thank you
Ryan