change the black header color + align: center the sticky header

hi everyone !
i need some help with the black header, I’d like to change the color so I put :
#page-header {background-color: #cecece ; }
but it’s not working…maybe it’s not called page-header ? I can’t find any other name :/

I also want to align : center the sticky header :
#cenote-sticky-header {background-color : white; text-align: center}
is not working

what am I missing ? I’m a beginner, here it’s 3am i’m half desperate, half tired >_<

I’m not fluent in English, I hope you’ll understant what I mean 🙂

thanks !!

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