Child theme issue?

Hello, i have a problem with my child theme that i created from FlaOn parent theme. In that child theme i only have one style.css file. When i click on pages from the menu, all the text become bigger. Sometimes i have to reload the site so that the original size will come back. I have jigoshop plugin installed, i tried to desactive it to see if this plugin causes this problem but it’s the same. I tried to activate the parent theme instead and this issue is gone. No text changing-size problem. I can’t figure out what to do and appreciate any help. That’s the link of the site: https://www.ultralife.se
Another issue regarding the FlatOn theme is that the slider is not showing up. Neither from the parent theme nor from the child. I tested to activate that theme to another old site i have, and the slider is there.
Thank you.