Re: show sidebar on single post pages?
You must validate the page CSS can not correctly parse the DOM / markup and know where to attach it’s rules to when there are markup errors.
You have non legal characters as literals, probably from copy pasting. Run through the major elements token identifiers and make sure they are all correct and proper “” marks
With that corrected you should find that your rulesets now can apply themselves to elements or tokens which they can recognise