WICKET-6920 Improve the examples to use the browser's light/dark mode

(cherry picked from commit 6666f9ad8a78b1213b8eb36782b9b4fc069bc1ac)
diff --git a/wicket-examples/src/main/resources/org/apache/wicket/examples/style.css b/wicket-examples/src/main/resources/org/apache/wicket/examples/style.css
index 7f4cad8..fed53be 100644
--- a/wicket-examples/src/main/resources/org/apache/wicket/examples/style.css
+++ b/wicket-examples/src/main/resources/org/apache/wicket/examples/style.css
@@ -20,7 +20,9 @@
   border: 0;
   font-size: 100%;
   font: inherit;
-  vertical-align: baseline; }
+  vertical-align: baseline;
+  color-scheme: light dark
+}
 
 *,
 *:after,
@@ -40,7 +42,6 @@
   text-shadow: none; }
 
 html {
-  color: #3f4542;
   font: 300 15px "Source Sans Pro", sans-serif;
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
@@ -1413,4 +1414,4 @@
 
 .light-grey {
 	background-color: lightgrey;
-}
\ No newline at end of file
+}