docs(css): Remove font size tweaks

Author: tony

docs/_static/css/custom.css

@@ -1,19 +1,16 @@
 h2 {
-  font-size: 2rem;
   margin-bottom: 1.25rem;
   margin-top: 1.25rem;
   scroll-margin-top: 0.5rem;
 }
 
 h3 {
-  font-size: 1.5rem;
   margin-bottom: 1.25rem;
   margin-top: 1.25rem;
   scroll-margin-top: 0.5rem;
 }
 
 h4 {
-  font-size: 1.25rem;
   margin-bottom: 1.25rem;
   scroll-margin-top: 0.5rem;
 }