How do I change the width and height (dimensions) of my site

Hello,

I am new to joomla, and I have been creating my web page for my business for a months now. I have 2 questions: How do I change the width and height (dimensions) of the web site in mobile version. Or how do I set up a specific zoom for mobile version of my responsive site. Right now, I am trying to figure it out by using inspect element and then try to find it in my "mj" folder where the plugin Mobile joomla is installed. However I am not sure where to find the code that is responsible for this option.
The second issue I have, is the fact that my main image under the menu is not showing in the mobile version, I guess it has to do with the code as well.
Heres my site, In order to see the issue, you have to acces the site via your mobile device.
herbavitas.ba/

Could You help me?

Files in the media/mj directory are generated automatically by merging and minifying original CSS and JS files. So, that files shouldn't be edited (as they may be be re-generated again, and all changes will be overwritten). If you need to change your CSS, disable Server-Side Optimization in the Advanced settings of Mobile extension, do whatever you need, and enable optimization again.

As to the image, most likely it's a conflict between your slideshow extension and lazy image loading in Mobile. Try do disable Lazy Load in the Advanced settings.