What are the ways to customize the design of an ios/android application?

Question

Android

The question is theoretical. We have a simple application, one screen, two buttons, one input field and a table (accordion), all these elements are standard. But I have a photo of how it should look, in principle, nothing over natural, rounded corners, gradient fill, a circle as a marker. In what way does the appearance change, like css, do all elements have a certain set of properties by changing which I can change the view or do I just need to specify an image for the element?
PS: If it's not difficult, give an example or a link to an example, such as making a button with round edges, gradients and, for example, a circle in front of the text.

Answer 1

Something some kind of water and not a question. The css analogue for android is styles and themes, which are also described in a separate file and control the appearance developer.android.com/guide/topics/ui/themes.html . How to make rounded edges stackoverflow.com/questions/16161448/how-to-make-l...

Answer 2

No problem, we'll google for you!
stackoverflow.com/questions/7984500/how-to-make-cu...
robots.thoughtbot.com/designing-for-ios-taming-uibutton