Update Build-CSS.ps1

Removed welcome.css

Author: jd-code76

dev_tools/Build-CSS.ps1

@@ -10,7 +10,6 @@ $FileOrder = @(
     "variables.css",
     "reset.css",
     "layout.css",
-    "welcome.css", 
     "sidebar.css",
     "reference-panel.css",
     "resize-handles.css",