This normally happens when you add any iframe code in the Muse design.
If you are using any 3rd party code which is creating an iframe then you need to style the iframe code.
However if this is a default Muse page without any 3rd party widget or iframe code, I will suggest you to publish the file and let us know the live link here so that we can look to the site codes.
Thanks for the answer.
It would be nice to solve this problem, what happens when I use the MASTER PAGES.
The following is a link to the files.
Delete this widget
...I want to draw your attention - your website is incorrectly built as responsive. Breakpoints is not set by the screens resolutions. They are set only when the design breaks. Between breakpoints your site is broken - this should not be. On the master page, there is no need to use as many breakpoints. I think you should look closely at this tutorials Responsive web design in Adobe Muse | Adobe Muse CC tutorials