The Directive @media SCSS and @extend how?

Good day,
there is such scss
@extend .size50;

@media (max-width: 992px){
@extend .size20 ;

at the beginning

But still when resolution is less than 992px the font size of 50 px.The scope does not work in the course...tell me how to make a media request.Thank you
June 14th 19 at 20:41

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