Style and theme in android

i think the the developer document of android is very good！So it is nessarry you speed some time to read it! You can learn more you don't know exactly.

https://developer.android.com/guide/topics/ui/themes.html


Remember, a style that you want to use as an Activity or application theme is defined in XML exactly the same as a style for a View.   A style such as the one defined above can be applied as a style for a single View or as a theme for an entire Activity or application. 

First: 
I think style the most importment is that, when you write the same component ,  you can reuse you write the style. you don't need to write the same code to the component .

一般追求的不同， you can get you want in android. So you must to know what you want to get!