Simply said you need to add @media to your scss file and define the screen size. Then within the scope of the media query you can create/override classes or apply styling directly.
FYI: Mendix provides different screen sizes out of the box which you can use:
//== Media queries breakpoints
//## Define the breakpoints at which your layout will change, adapting to different screen sizes.
$screen-xs: 480px !default;
$screen-sm: 576px !default;
$screen-md: 768px !default;
$screen-lg: 992px !default;
$screen-xl: 1200px !default;
// So media queries don't overlap when required, provide a maximum (used for max-width)
$screen-xs-max: calc(#{$screen-sm} - 1px) !default;
$screen-sm-max: calc(#{$screen-md} - 1px) !default;
$screen-md-max: calc(#{$screen-lg} - 1px) !default;
$screen-lg-max: calc(#{$screen-xl} - 1px) !default;
below you can find an example:
@mixin layout-atlas-responsive() {
// Topbar variant
.layout-atlas-responsive-topbar {
.region-topbar {
padding: 0 $spacing-medium;
@media (max-width: $screen-sm-max) {
padding: 0 $spacing-small;
}
}
}
}
You can refer to the docs for more information. Hope that answered your question