Yellow is no longer used as a button color in the staff client for normal actions such as closing dialogs that do not involve a condition that actually requires a warning.
Instead, light grey is used as a default color for buttons that do secondary actions, with a variant that includes red upon hover or activation for actions that remove data or clear form input.
The `btn-warning` CSS class should be avoided in the staff interface unless needed for actions that truly require a warning. Instead, `btn-normal` should be used for secondary actions such as closing a dialog and `btn-destroy` for actions that would remove or clear data.
See Bug #2023803 Stop using yellow buttons for normal operations