Create a table with the amount of rows required for tab headings. Give this table the class of "tabs" (under the "Properties > Appearance" tab).
Create your text popups, and give them all class of "tab_content", and individually give them the class "tab_content01", "tab_content02", etc - depending on which tab number it is. An example of a complete tab class is "tab_content tab_content01".
If you need to group assets together to make the popup (text, images, etc), make sure they ALL have these classes attached.
10 tabs have been set up in "custom.js", but if you need more, please read below.
Go to "custom.js" in the "extern" folder - and within the "tabs" section - copy and paste where specified to create new tab action.
Update the numbering in the above code to reflect the new tab number (required in 2 places - see comments in "custom.js").
Please note - all styles will be added when published (white text, red background, etc).