Meanwhile I unfixed the sidebar and header and instead fixed the widgets using
padding: 25px 0px;
The padding of the page widget needed to be adjusted so it shouldn't overlap the search. Is there any way to just tell it to stay below the widget above it so that it can stay below one even if the size varies (such as a posts widget which will change based on post titles)?
I am starting with the left sidebar and will apply my learning to the right sidebar later.
Also, is there a way to get the widgets to move up when scrolling down so as not to leave a blank space above them but have them stop at the top so that they should not go off the page and leave the whole sidebar blank?