docs: increase header spacing

Author: hassankhan

docs/static/styles/_typography.scss

@@ -66,19 +66,21 @@ h1 {
 h2 {
   font-size: 1.5rem;
   line-height: 2rem;
+  margin-top: 3.5rem;
   margin-bottom: 16px;
 }
 
 h3 {
   font-size: 1.25rem;
   line-height: 1.875rem;
-  margin-top: 24px;
+  margin-top: 2.5rem;
   margin-bottom: 8px;
 }
 
 h4 {
   font-size: 1.125rem;
   line-height: 1.75rem;
+  margin-top: 1.5rem;
   margin-bottom: 8px;
 }