Mobile: bump h2 to 36px, center red accent bar under all h2s

Author: MMesch

src/css/custom.css

@@ -186,7 +186,7 @@ ul {
 
   h2 {
     font-family: var(--ifm-font-family-display);
-    font-size: 30px;
+    font-size: 36px;
     font-style: normal;
     font-weight: 800;
     line-height: 115%;
@@ -278,6 +278,13 @@ ul {
   margin-right: auto;
 }
 
+@media (max-width: 996px) {
+  .page-content h2::after {
+    margin-left: auto;
+    margin-right: auto;
+  }
+}
+
 /* No red bar on dark-background sections */
 [class*="section_dark"] .page-content h2::after {
   display: none;