Apply suggestions from code review

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: JelleZijlstra

peps/pep-0834.rst

@@ -65,7 +65,7 @@ understand that certain base classes or decorators radically change what a class
 does, instead of putting the special behavior of these constructs front and center in the
 syntax.
 
-This PEP proposes a flexible new syntax to declare these constructs using *class builders*:
+This PEP proposes a flexible new syntax to declare these constructs using *class builders*::
 
     builder Simple:
         ...
@@ -93,7 +93,10 @@ Syntax
 ------
 
 The grammar for class definitions is extended to allow a name before the
-class name::
+class name:
+
+.. code-block:: peg
+
 
     class_def_raw:
         | 'class' NAME type_params? ['(' arguments? ')'] ':' block