Use Simple CSS to adjust width of container of the Page

Hi, guys,

My site's layout is Container/Sidebar. Container width is 1.100 px.

I have few pages, which have not Sidebars, just a Container (blank page).
If i put some text it looks very wide, 1.100 px.

Is there any way to adjust width of Container only on a particular Page?

***
I use Simple CSS plugin.
I use this code:

button {
padding: 8px 18px;
}

to overwrite default buttons's appearance. (Tom showed me that)
I dont know, if im wrong or not, but my idea is to overwrite Container width of a particular Page the same way i did it to overwrite Button's appearance.

***
After installing Simple CSS plugin, every Page/Post has a "Box" with a window to write something in.
It goes after page/post content, comments etc.

Is there any way to use Simple CSS plugin, which window is inside that particular Page/Post (and any Page/Post) to adjust width of the Container on that particular Page?

or maybe there is another way to adjust Page's width.

Thanks.