Add h3 and h4 styling

Author: PoojaB26

src/css/custom.css

@@ -85,12 +85,19 @@ h2 {
 }
 
 h3 {
-  color:var(--graytext);
+  color:var(--black-700);
   font-size: 20px;
-  font-weight: 200;
+  font-weight: 700;
 
 }
 
+h4 {
+  color:var(--black-700);
+  font-size: 18px;
+  font-weight: 500;
+
+}
+
 
 p {
   font-size: 16px;