Submenu Opened

I would like to know how to keep the submenu opened. Once i click on a submenu element, how to see the menu opened with the submenu element on dark.

I am looking for the effect that you can find in the url that i have include at Link to the page you need help with: http://cersani.com/ceramica/

My website is: http://albergueweb1.uva.es/fyluva/administracion-y-servicios/mantenimiento/

(Lateral menu)

The page I need help with: [log in to see the link]