Check out example codes for "media screen scss mixin". It will help you in understanding the concepts better.

Code Example 1

// respond is the name of your mixin

    @mixin respond ($breakpoint) {

        // $breakpoint is simply a variable that can have several values

        @if $breakpoint==tablet {

            // here `laptop` is the value of $breakpoint
            // when call laptop, we mean the following piece of code        

        @media only screen and (max-width: 600px) {
          @content;
        }
      }

      @if $breakpoint==mobile {
        @media only screen and (max-width: 480px) {
          @content;
        }
      }
    }

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