Text runs off the right edge of page in mobile portrait mode
I am using Dawn on Drupal 7.
The site looks fine on desktop and on mobile in landscape mode (iPhone 6).
However, in portrait mode, some of the text contained in blocks or the recent posts blog widget runs off the right edge of the screen. See red boxes in attachment. I have Prescript 1, 2, and 3 set as span4 in the Regions section, and Prescript 4 as none.
How can I fix this?