change highlight theme

.gitignore

@@ -104,3 +104,5 @@ venv.bak/
 .mypy_cache/
 
 **/yindex.html
+
+**/.idea

index.html

@@ -430,7 +430,7 @@
 ]
 
 .right-column[
-```
+```Java
 private static class GracefulShutdown implements
 TomcatConnectorCustomizer,
 ApplicationListener<ContextClosedEvent> {
@@ -472,28 +472,33 @@
 name: zen
 # [The Zen of Python](https://www.python.org/dev/peps/pep-0020/#id3)
 ---
+name: zen-values
+class: middle
+
+A collection of 19 "guiding principles" that influence the design of the Python programming language.
+
 
 ```python
 > python3 -m this
   The Zen of Python, by Tim Peters
 
-  Beautiful is better than ugly.
-  Explicit is better than implicit.
-  Simple is better than complex.
+  `Beautiful is better than ugly.`
+  `Explicit is better than implicit.`
+  `Simple is better than complex.`
   Complex is better than complicated.
   Flat is better than nested.
   Sparse is better than dense.
-  Readability counts.
+  `Readability counts.``
   Special cases aren't special enough to break the rules.
   Although practicality beats purity.
-  Errors should never pass silently.
+  `Errors should never pass silently.`
   Unless explicitly silenced.
   In the face of ambiguity, refuse the temptation to guess.
   There should be one-- and preferably only one --obvious way to do it.
   Although that way may not be obvious at first unless you're Dutch.
   Now is better than never.
   Although never is often better than *right* now.
-  If the implementation is hard to explain, it's a bad idea.
+  `If the implementation is hard to explain, it's a bad idea.`
   If the implementation is easy to explain, it may be a good idea.
   Namespaces are one honking great idea -- let's do more of those!
 ```
@@ -514,7 +519,7 @@
     <script>
       var slideshow = remark.create({
         highlightLanguage: 'python',
-        highlightStyle: 'darcula',
+        highlightStyle: 'dracula',
         highlightLines: true,
         highlightSpans: true
       });