Sometimes it’s tempting to use webkit’s drawing features, like -webkit-gradient, when it’s not actually necessary - maintaining images and dealing with Photoshop and drawing tools can be a hassle. However, using CSS for those tasks moves that hassle from the designer’s computer to the target’s CPU. Gradients, shadows, and other decorations in CSS should be used only when necessary (. when the shape is dynamic based on the content) - **otherwise, static images are always faster**. On very low-end platforms, it’s even advised to use static images for some of the text if possible.
When it comes to UI, Ionic shows its potential. Ionic’s true beauty is its simplicity. In almost Google-like (but not Android-like) style it uses the existing HTML5 and CSS3 capabilities to deliver fast experiences. The speed is exactly in its simplicity – no unnecessary shadows, rounded corners, gradients but just flat, clean simple, powerful, unadulterated HTML5. Ionic doesn’t promise you native-looking UI, but it does deliver very fast and consistent interface, even on the devices you considered to be slow with rendering HTML5 apps.