When I first delved into coding with react-native, I encountered a similar issue when applying the same CSS style.
Before diving in, it's important to carefully read through the documentation to grasp the concept of flex.
Flex dictates how items will vie for available space along the primary axis. Typically, setting your app container to flex:1 allocates all screen height. Space is distributed based on each element's flex property. For instance, if the red, yellow, and green views are children within the container view set to flex:1, their respective flex values - 1, 2, and 3, determine their share of space (1/6, 2/6, 3/6). It's all about proportion.
To gain further clarity on the above explanation, refer to this helpful post on medium.com.
Additionally, eliminating the use of dimension is key when developing apps with react-native.
MainContainer: {
height: '100%',
width: '100%',
backgroundColor: '#fff',
}
This snippet suffices for designing the main container. Also, opt for scrollView when incorporating input fields.
Hopefully, my response sheds light on your query.