Size of menu and header of the menu

Hi I would want to decrease tue size of the font for the menu and sub-menu I found to decrease the size of the menu by these add-on on CSS customize: #fixed-header-top ul li a { padding: 12px 15px; font-size: 12px; } But these decrease the font but not the part "header" of the menu In the same way, how to decrease the text of the sub-menu and the band of the sub-menu My website: fredericvoyage.fr Thanks for your help Frederic