Where to change HMTL or CSS to make text body wider

[MonikaBarget]

I have used Time Machine to create the following deployment:

https://ieg-dhr.github.io/DigiKAR_Projektseminar/

Now I want to make the container with the text body wider, but I could not find the relevant settings in either the HTML nor the CSS files.

Could you point me into the right direction?

[MonikaBarget]

I found the following section in the CSS stylesheet that may be what I am looking for:

#container {
  border: 1px solid #2a2a2a;
  background: #ddd url(../images/pattern.png);
  box-shadow: 0 0 5px #b1b1b1;
}