Sidebar Problem With Twenty Eleven Child After Updating to WP 4.5

Since updating to WP 4.5 yesterday the sidebar displays under the main content on a computer screen instead of to the right side. The site uses a lightly customized child theme of Twenty Eleven, mainly for the images in the menus. The site has been working fine for several years. We also just added a header.php to the child theme to do some Google Analytics. Removing the Google Analytics changes nothing. Disabling all plugins makes no difference. Validating the HTML reveals nothing I could see as causing the problem. None of my child theme CSS changes the layout, AFAIK, but I am not particularly skilled as CSS. The site is https://tiferetisrael.org Thanks for any help.