Fix rhythm heading cascade issue (#1866)

Author: tylersticka

.changeset/cuddly-dryers-build.md

@@ -0,0 +1,5 @@
+---
+'@cloudfour/patterns': patch
+---
+
+Fix headings in Rhythm objects not respecting cascade of `--rhythm` custom property

src/mixins/_spacing.scss

@@ -71,7 +71,7 @@ $fluid-spacing-inline-negative: fluid.fluid-clamp(
     > * + h5,
     > * + h6,
     > * + [class*='heading'] {
-      margin-block-start: var(--rhythm-headings);
+      margin-block-start: var(--rhythm-headings, var(--rhythm));
     }
   }
 }

src/objects/rhythm/demo/sections.twig

@@ -7,6 +7,9 @@
     } only %}
       {% block content %}
         {% for i in 1..3 %}
+          {% if i == 2 %}
+            <h2>More Sections Below</h2>
+          {% endif %}
           <div>
             <h3>Section {{i}}</h3>
             <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum quam tellus, auctor non faucibus consequat, dictum et dui. Praesent vitae magna sit amet odio egestas semper. Duis nec tellus ligula. Pellentesque mollis varius pulvinar. Suspendisse eu ultrices quam. In dignissim felis efficitur lorem porttitor porttitor. Aliquam maximus tempus erat ut sagittis.</p>

src/objects/rhythm/rhythm.scss

@@ -3,7 +3,6 @@
 
 :root {
   --rhythm: #{size.$rhythm-default};
-  --rhythm-headings: var(--rhythm);
 }
 
 .o-rhythm {