To change the bottom border color of Textield you can use border-width
CSS properties (or directly their respective inline ones
The above CSS will result in red bottom color on both iOS and Android. A real example is demonstrated in this test application
Regarding the second part of your question (" focus bottom border color of text field
") I am not entirely sure that I am understanding the question but if you need to manually focus the TextField (invoke the keyboard) you can call focus method with a small amount of timeout (as the keyboard can be triggered only after the whole UI is rendered). For example, I have demonstrated the focus method here
while using the loaded event
for the TextField. Note that this would trigger the keyboard on a real iOS device but might not trigger it on simulators.