I've added a darkmode setting to my website, and I made a cookie using javascript so it's saved for when you come back, everything works like a charm until you close the browser window.
var cookie = document.cookie = 'darkmode=false; SameSite=none; Secure';
Is there a way to make the cookie stay for as long as possible?
You should add expires and/or max-age for the cookie. Check the documentation for more information.
var cookie = document.cookie = 'darkmode=false; max-age=31536000; expires=Fri, 31 Dec 9999 23:59:59 GMT; SameSite=none; Secure';