menu options

Hi,
three quick problems:
I have a problem with the mobile menu of my website. it doesn’t show when clicked, or when it does show really briefly and then disappears again.

Then i would like to change the style of the dropdownmenu child. The background-color to #18b6c8 and the text to #fff. when hovered it should be a slighter lighter background-color with dark font.

Is it possible to add an arrow after the parent of the drop down menu?

This is the URL of the webpage: http://www.foto-spiegel.nl
Thanks in advance