I had installed the bb press and the forum window is very small.You can check it here.

[@peter-hamilton Participant 7 years, 1 month ago]

You could use CSS to make the width of articles 100%

.article {width: 100%;}

You can use google Chrome to test/alter CSS to see what you need to do to fix things.
Use right mouse button on an element on the screen and press “inspect”, then a window opens where you can play with CSS.

You do have a child-theme I hope?

[@johncarlo013 Participant 7 years, 1 month ago]

Try this one hope it will help
Open your style.css, go to line 1089 and write this:

#content {
float: left;
width: 68%;
}

[@johncarlo013 Participant 7 years, 1 month ago]

Also try this one also to see more simple tutorial about bbpress like globe promos and smat promos