fix highlighting of ast nodes in traceback.

Using ansi mean it will follow terminal colorscheme

IPython/core/ultratb.py

@@ -826,8 +826,8 b' class VerboseTB(TBTools):'
         after = context // 2
         before = context - after
         if self.has_colors:
-            style = get_style_by_name('default')
-            style = stack_data.style_with_executing_node(style, 'bg:#00005f')
+            style = get_style_by_name("default")
+            style = stack_data.style_with_executing_node(style, "bg:ansiyellow")
             formatter = Terminal256Formatter(style=style)
         else:
             formatter = None