Safari not rendering web-page correctly
On my machine (iMac late 2015, macOS 10.13.6, Safari 11.1.2), the cause of the bad rendering was the AdBlock extension. I removed it, restarted Safari, and Safari rendered correctly. I then re-downloaded AdBlock, and Safari continues to render correctly. 

I moved too fast doing this, and didn't note the version number of the AdBlock I removed, so don't know if the not-working AdBlock I removed was the currently-downloading version. In any event, the just-downloaded version doesn't interfere with Safari's rendering.