To change the font size in the menu, you have to go to: Betheme > Theme Options > Fonts > Size & Style, and there you can modify the "Main Menu" font size.
But if you are talking about that "Dienstleistungen" text you must change the "H1" font size in the same section. https://prnt.sc/v3u2j9
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To change this link color go to: Betheme > Theme Options > Colors > Headings, and modify "Heading H5 color".
https://prnt.sc/v3so1y
Thanks
https://prnt.sc/v3u2j9
Thanks