CSS help please

I want to be able to edit things in the CSS - simple things like chnging the size of font, etc - this is something I am used to doing (normally use iThemes Builder) I have searched the forumsand found that I needed to copy a css from the parent theme to the child theme (child is activated, parent never has been) - I put a copy of the layout.css into the child theme and I can see it and edit it successfully in the editor area - I am testing this by picking a heading and changing the font size to something rediculous so that I can see on the live site if I am indeed editing the correct area.

As I said, the edits I make in the childs layout.css are taking and saving but the changes are not happening on the site??

So have I put this layout.css in the wrong place? should I have copied it's entire contents and put it inside the child style.css? if so, where should I put it?

Any help to end my frustration appreciated.
Thanks
Sue

PS/Edit - sorry should have mentioned, using Network Theme - site is in maintenance mode but can open it up if someone wants the link.