See apps/index.css. There are a series of @media queries on aspect ratio. Those width percentages are based on full screen specs of various devices. They do not take into account a browser window that is not maximized, and even maximized vs full screen is different. They are also not necessarily set to the best value.
Is there a some semi-standard method for sizing a centered column of text based on the available width and maybe font size? A set of guidelines? My web searches have yielded nothing of use. What do all the news sites and WordPress pages do?