Include Twig file without providing file extension

I am new to design template templates. I am trying to include some twig file in another twig file. I am using the following code to enable it,

{% include 'layout/css.html.twig' %}

      

        
        
        
      

    

But for inclusion, I want to include the file without adding the extension to it. Where should this configuration be used to use the above include as shown below?

{% include '/twig/front/layout/css' %}