Can′t Affect Changes with Child Theme

I created a child theme for which twentytwelve is the parent.
I know that the child theme is working because if modify:

@import url(“../twentytwelve/style.css”); to say
@import url(“./twentytwelve/style.css”); (erase one button)

After saving I see my site with a broken desing (NO CSS)

So using chrome I discovered that if modify:

/* Page structure */
.site {
	padding: 0 24px;
	padding: 0 1.714285714rem;
	background-color: none;
}/*I changed the value of background-color from "fff" to none */

On the parent and I get the exact result I want.
So I copied that and pasted it in my child theme but NO CHAGE takes place. If I go and make this change on the parent I do get the effect I want but I do not want to make any changes to the parent theme. Instead I want to know what I am doing wrong for this not to work through my child theme.

Thanks. Agustin Uribe