Hi Dary,
Yes we have change some code as well as script for the responsive menu which effect the header section. However, It will not change the appearance of your site and we have checked it before pushing it to live.
May you have some custom css code, child theme or changed theme code.
Also we can not visit the link that you have shared. Can you please check the link.
Don’t be worry you need not have to change the theme, we are here to help you.
Just provide us the exact site link and we will see what is the issue and let you know?
Thank you!