CSS: Avoid horizontal scrolling
I view at least half the written content I consume via my mobile phone, which belongs to the class of phones with a slightly smaller than average screen. In fact, it’s width as reported by the Firefox and Chrome viewport simulators is 375 pixels wide, small but not tiny. And yet many websites I visit hinder my mobile viewing experience because of a rather simple issue: horizontal scrolling.
Source: CSS: Avoid horizontal scrolling, an article by Ben Fiedler.