The screen when editing and viewing on mobile are different. Help me

1.https://ifh.cc/v-o75GjC
i have a problem
If you write on the web and set it on mobile and look at the screen, there is a blank space on the side.
The problem is that, unlike what you see on the web, when you access the site from a smartphone, the text fills the screen with no space.

2.https://ifh.cc/v-tqgqo1
I need help The screen is different from the web screen I wrote on my PC and the screen I saw on my smartphone, so it’s a problem now

The screen that you write and check directly in WordPress is different from the screen you see directly on the mobile screen

I wrote down the site address. Please access the site with your smartphone. You can see that there are no side blanks on the mobile screen.

I left the administrator ID and password as answered.
What I want is to look the same on mobile when set up like customization
To put it simply, like the attached URL image, I wish there were blank spaces on both sides when connected with a smartphone.
The screen when editing and viewing on mobile are different. Help me