2015Theme

I am new to wordpress so excuse the newbie question.

I did not like the width of the sidebar in the 2015theme, because it needs to be shrunk some.

I did not see a way to do that except to find where the width and other parts are in the CSS editor. The editor has miles and miles of code, so I was looking for a way to search the code for a keyword such as width to see what it had.

Did I miss something or can I not find it that way?

Bruce