You can edit the content of jQuery Mobile pages by editing the HTML as we have just seen. However, you can customize the look of jQuery Mobile pages by changing the CSS styles associated with different jQuery Mobile objects.
This is complicated. The complications arise from the fact that there are a gazillion (roughly speaking) CSS styles that make up the jQuery Mobile style sheet.
The developers of jQuery Mobile have addressed this challenge by providing a set of themes. Themes are a formatting tool used in different kinds of auto-generated content environments. Blog generators such as WordPress or Drupal (these programs can be stretched beyond designing blogs, but that is their essential role) provide developers with a variety of themes that apply sets of colors, fonts, and background images.
As such, themes are, in general, something of an anathema to creative web page designers who want uniquely formatted pages, not paint-by-numbers pages that are...