how to give height and width using dimensions in react-native code example

Example 1: width 100% react native

import { Dimensions } from 'react-native';

width: ${(Dimensions.get('window').width)}px;

Example 2: how to take 100% width in react native

header : {
	height : 100,
  	backgroundColor: "favorite color",
    alignSelf: "stretch",
}