How to make the main menu stand out more against a header picture background

Hi, My new site https://paulovancuijck.nl/staging2/ looks great with the slider pictures. However the text of the main menu - depending on the slider or header picture - isn't always clearly visible. Are there options to give the main menu text more contrast against the background, for instance with an outline, shadow or something? And it possible to increase the size of the font of the main menu? And where can I change the colour of it the main menu text? Looking forward to your suggestions. Regards, Paulo