title: Populate one dropdown list based on the selection of other dropdown list
body: <p>I want to create two drop down lists, category and item.</p>
  
  <p>If I select one of the categories named car, then item drop down list should have Honda, Volvo, Nissan.</p>
  
  <p>If I select one of the categories named phone, then item drop down list should have this iPhone, Samsung, Nokia.</p>
  
  <p>How can I do this?
  I know that I can't do it with plain HTML.</p>