title: Drupal 8 How to create custom block in a theme
body: <p>I have created a custom theme and added regions. I want to create and assign a custom block to the regions. How can I do it?</p>
  
  <p>As an experimental purpose I have created a folder named 'blocks' in path /themes/custom_theme/templates and named the block 'block--regionname.twig.html'. But no hope. Please advice. I think i'm on a wrong track.</p>