How to Get a CSS Selector?
With the Ocean Stick Anything plugin, you can stick what you want, but you need to add a CSS selector in the Elements field in Theme Panel > Stick Elements.
In my example, I want to stick my sidebar. So, I do a Right Click > Inspect Element on my sidebar like below:
In the screenshot below, you can see the source code for the sidebar, there is one ID "right-sidebar" and some classes "sidebar-container widget-area sidebar-primary":
Now, as the sidebar as an ID attribute and some classes, you can add "#right-sidebar" or one of the classes ".widget-area" in the Elements field in Theme Panel > Stick Elements:
Note: For the CSS selector, if you take the "id" attribute, you need to add "#" before the selector and if you take a class, you need to add a dot "." before the selector.