The text seems to be wrapped at a width of 80 characters or so. Instead, it should fill the full width of the webview. Tested in kate.
Thanks for the report. The behaviour you see is intended though, with readability in mind, and defined as such in the default CSS stylesheet used. So closing this bug as WONTFIX. But I support and share the desire for being able to customize the behaviour as personally preferred. Right now the CSS used is hard-coded, though ideally one should be able to override this. Please subscribe to https://bugs.kde.org/show_bug.cgi?id=385219 which is about that very feature.
Ok I subscribed to the other bug. But still for the default stylesheet I would suggest at least to center the text if you want to keep that hard limit. As it is now looks pretty ugly with all that white space on the right side (see attachment).
Created attachment 108115 [details] Word wrap and left alignment
Agreed, centering would be a good idea. Filed as https://bugs.kde.org/show_bug.cgi?id=385263