What is the best way to create a responsive menu using only CSS and HTML?

[SubhanUllah]

 

Using media queries:

@media only screen and (min-width: 320px) and (max-width: 768px) { 
     .nav { 
         width:100%; 
    } 
     .nav-item { 
         width:100%; 
         float:none; 
    } 
}