Headings Font Size and Spacing

Hello,

I would like to be able to modify 2 things:

1) Change the Headings Font Family for headings within articles/posts (so NOT the title post nor any other heading)
2) Change the spacing above and below for headings within articles/posts (so NOT the title post nor any other heading)

What I have tried already:
I have tried using the following rule in the child theme:

h3 {
margin-top:10px;
margin-bottom:1px;
font-family:”Open Sans”, sans-serif;
}

As for the margins, I must be using the wrong code. As for the font-family, it seems that the parameters set in Appearance/Typography/Heading Font Family – overwrite this CSS rule.