Change the text size of the story (if the story’s channel supports it):
Make the text bigger: Press Option-Command-Plus Sign (+) until the text is the size you want.
Make the text smaller: Press Option-Command-Minus Sign (-) until the text is the size you want.
The text size is changed for all stories from that channel.
If you want to reset the content to its actual size, press Shift-Command-0 (zero).