The Web Field Manual is a curated list of resources focused on documenting only the best knowledge for designing experiences and interfaces on the web.
What if you want to add one post from a particular category to the sidebar in Wordpress? I found this code that helped me, on stackoverflow
The tutorial shows a little jQuery code snippet, which sticks the horizontal menu onto the top of your page when you are scrolling down to read the page contents. This feature is very useful even in the mobile version of your webpages. Your user will never feel lost browsing your pages.