“Think of CSS as working entirely with paragraph styles. Altering one item on the fly is cumbersome. CSS works best when applied to a whole classification of images or words (hence the ‘class’ attribute in HTML).”
“Responsive themes are as varied as the problems they are meant to solve. Not all are created with the same technique, features or attention to detail. Aesthetics aside, how should someone choose a theme?”
In searching for interesting patterns, designers sometimes pass over basic shapes in favor of more complex geometrics. But simpler is often better. The trick is to pay attention more to how shapes interact than to how a shape looks on its own. The concepts are simple, but the choices are endless.