css.css

:root{
    --size: 375;
}

@media (min-width: 769px) {
    :root{
        --size: 1440;
    }
}

@mixin fluid($properties, $value) {
    @each $property in $properties {
        #{$property}: calc(#{$value} * (100vw / var(--size)));
    }
}

html{
    @include fluid(font-size, 10);
}

/* 
  Since I use a fluid html font size, based on the screen width, 
  everything that uses REM units will scale perfectly with the size of the screen.
*/

.something{
  font-size: 1rem;
  margin: 1rem;
}