[mod] simple client: pygments.less - switched dark theme to monokai

Compared to ``lightbulb`` theme we used in the past for the dark theme, the
``monokai`` has a better contrast [1].

BTW, the result list of SearXNG should not act as a code-checker: The border &
color of class ``.err`` (used for syntax errors) has been removed / code
snippets are often not well formed nor valid code and the rendering of such code
fragments as errors obscures the view on the code snippet.

[1] https://pygments.org/styles/

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

client/simple/src/less/code.less

@@ -30,6 +30,12 @@
     span.linenos {
       color: var(--color-line-number);
     }
+
+    .err {
+      // The code view in the result list should not act as a code-checker.
+      border: none;
+      color: inherit;
+    }
   }
 }