Improve layout of featured cards on small screens

Temp style overrides to the image card component from the gem to:

- Ensure the space between the image card and the text remains at 15px on mobile, this was previously 30px on mobile.
- Ensure the featured image cards have 15px padding to the left and right when this screen width is =< 319px.

app/assets/stylesheets/views/_homepage.scss

@@ -211,6 +211,24 @@
 
 .homepage-section--promotion-slots {
   padding-top: govuk-spacing(6);
+
+  // temp style overrides, will need to update the image-card component in the gem
+  // so these can be removed
+  .gem-c-image-card {
+    @include govuk-media-query($until: "mobile") {
+      padding: 0 govuk-spacing(3);
+    }
+  }
+
+  // temp override to remove the top border
+  .gem-c-image-card__image {
+    border-top: none;
+  }
+
+  // temp override to reduce white space on mobile between image and text
+  .gem-c-image-card__text-wrapper.gem-c-image-card__text-wrapper--two-thirds {
+    padding-left: 0;
+  }
 }
 
 .homepage-section--links-and-search {
@@ -307,10 +325,3 @@
     padding-right: govuk-spacing(4);
   }
 }
-
-// temp override to remove the top border,
-// will need to update the image-card component in the gem
-// this can then be removed
-.homepage-section--promotion-slots .gem-c-image-card__image {
-  border-top: none;
-}