Small design adjustments

Increase bottom padding on buttons to 25px. Note that we only need 15px padding here, as another 10px comes from the invisible bottom border that improves high contrast mode presentation.

Add more spacing between the elements inside the button on mobile.

Fixes #2324

src/govuk/components/accordion/_index.scss

@@ -198,7 +198,7 @@
     .govuk-accordion__section-button {
       width: 100%;
 
-      padding: govuk-spacing(2) 0 govuk-spacing(1) 0;
+      padding: govuk-spacing(2) 0 govuk-spacing(3) 0;
 
       border: 0;
 
@@ -321,7 +321,11 @@
     // As a result this is applied to the pseudo element that has a display:block property to maintain Design
     .govuk-accordion__section-summary:before,
     .govuk-accordion__section-toggle:before {
-      margin-top: 8px;
+      margin-top: govuk-spacing(2);
+
+      @include govuk-media-query ($from: desktop) {
+        margin-top: 8px;
+      }
     }
 
     // Space between icon and text,