When you are including your mixin, you don’t need to use your variable name, just type in the property value like it’s normal css. So example
/* I created a mixin for backdrop-filter */
↓↓↓↓↓↓/* This is just a parameter */
@mixin backdrop-filter ($filter){
-webkit-backdrop-filter: $radius;
-moz-backdrop-filter: $radius;
-ms-backdrop-filter: $radius;
backdrop-filter: $radius;
}
/* Then I'm going to include it in my paragraph */
p {
@include backdrop-filter(blur(4x));
}