You must have the Experience Add-on to change the Search Layout appearance, and along with other add-ons, also allow you to to use the shortcode on SLP WP page.
These shortcodes only apply to the Search Layout admin setting when you have the appropriate Add-on installed and activated.
slp_search_element
This shortcode provides a simple mechanism to place standard search form elements on a custom search form layout, including the wrapping divs and classes around labels and input fields.
button Attribute
Places a search form button on the search form.