Update KeyCodeGlobalExample.razor.css to fix dark mode visuals (#1834)

The key text was hard to read in dark mode, changed CSS so text looks good in both modes.

Co-authored-by: Vincent Baaij <vnbaaij@outlook.com>

examples/Demo/Shared/Pages/KeyCode/Examples/KeyCodeGlobalExample.razor.css

@@ -11,6 +11,7 @@
     text-align: center;
     font-weight: bold;
     font-size: 14px;
+    color: black;
     cursor: pointer;
 }