Responsive template moves from side-to-side on iPhone

Hi, I use CatchBox Pro on my blog site, https://www.robertfairhead.com. When I access the site on my iPhone or my son's Galaxy s8, the resized, responsive template moves from side-to-side if you hold thumb on it and move it. It does not do this when resized for tablets, small or large. Obviously, there must be a CSS setting that fixes the resized template and I wondered if you could point me in the right direction? Please let me know if you need admin access to the theme and its settings. Regards, Robertf