title: Change TextField decoration onFocus in Flutter
body: <p>I would like to have a different <code>fillColor</code> for the <code>TextField</code> when it is in the focused state and a different one in the normal state. How to achieve this kind of behavior?</p>
  <p>Similarly, is it possible to customize other styles as well based on the state of the <code>TextField</code>?</p>
  <p>Edit:</p>
  <p>I was aiming for a color transition something in lines of this for mobile with flutter.</p>
  <p><a href="https://i.stack.imgur.com/Wwk3l.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Wwk3l.gif" alt="Searchbar transition" /></a></p>