Can't remove inline style from sidebar of Twenty Fifteen

Between the display widths of 955px and 1014px, the sidebar of my Child of Twenty Fifteen theme is supposed to show at the top of the page and I should be able to scroll down the page away from it, leaving it behind at the top of the page. However, the sidebar is acting fixed, so that the content on the page scrolls over it. It is behaving like a fixed background image.

Here is my site: https://soazseniorpride.org

Inspection via Chrome Developer Tool reveals this styling on the sidebar for this range of display size (955px-1014px):

<div id="sidebar" class="sidebar" style="position: fixed;"

If I change position to relative using the Chrome Developer Tool, the problem goes away. So it seems that there is an inline styling of the sidebar that is fixing it for just this range that I need to change to relative. But I am stumped about where to locate this inline styling in the files of the theme…

Can someone please enlighten me: Where should I look for an inline styling of the sidebar that is applicable only for a very specific range of display size?

Thank you in advance!