My desktop hamburger menu follows while scolling, but not the closing button! How do i fix this?

I have (with css help) created an transparent hamburger overlay menu on desktop version in squarespace. But my menu is sticking with the scrolling of the site. My x (closing button) is not scolling, but sticked to the header. So when scrolling, the menu can not be closed.. Can someone please help me with this

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Hi,

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