Tweak API css

docs/source/_static/api.css

-body {
-  font-size: 1.2rem;
-}
-
 .brand-heading {
   display: flex;
 }
@@ -21,21 +17,25 @@ body {
   margin-top: 0;
 }
 
+section h1 {
+  margin-left: 0;
+}
+
 h2 {
-  font-size: 45px;
+  font-size: 40px;
 }
 
 h3 {
-  font-size: 35px;
+  font-size: 30px;
 }
 
 h4 {
-  font-size: 30px;
+  font-size: 25px;
   margin-top: 40px;
 }
 
 p {
-  font-size: 1.3rem;
+  font-size: 1.2rem;
 }
 
 .details {