Thanks for your reply.
Yes you may make the necessary adjustments to the core files as needed but I highly suggest creating a child theme before applying these changes as a theme update could overwrite them.
You may use the following plugin to successfully create a Child Theme if needed
Child Theme Configurator
In regards to mobile viewports, you will need to edit the CSS for the respective media queries which can also be found in the style.css file.
As this is a more complex tweak which we do not cover in our general support you may opt to hire our developer to assist you with this as well.
Please let me know if there are any more questions that I can answer for you 🙂