How about an activity indicator? Framework 7 has a nice one. The F7 preloader is made with SVG and animated with CSS so it can be easily resized. Two options are available: the default is for light background and another one is for dark background. The HTML is pretty easy, just add a .preloader class to any element. For the dark background option, also add a .preloader-white class. Here are some examples:

Default:

White:

Big:

White:

Preloader also support all default color themes:

With app.showIndicator() you can call small overlay with indicator:

Open small indicator overlay

With app.showPreloader() you can call modal window with preloader:

Open preloader modal

With app.showPreloader('My text...') you can call it with custom title:

Open custom preloader