jQuery structure vs. theme CSS, what's the purpose?
The jquery-ui.structure.css file provides the structural CSS rules (such as margins and positioning), and the jquery-ui.theme.css file contains the theming rules (such as backgrounds, colors, and fonts). This setup allows you to easily change themes by swapping in new jquery-ui.theme.css files. You can also build a theme from scratch by building on top of jquery-ui.structure.css. The jquery-ui.css file contains both jquery-ui.structure.css and jquery-ui.theme.css.
I don't get the point of this, so basically `jquery-ui.css` = `jquery-ui.structure.css` + `jquery-ui.theme.css`, is it now recommended to include two CSS files instead of one for this modularity? I don't understand the reason why the jQuery UI team decided to do this.