How sidebar area can be expanded?

By default there is 85px spacing between #primary (content = 625px) and #secondary (sidebar = 250px)

So you can add at most 85px to 250px, but to leave a proper gutter which should be 40px ( same as main page’s padding ), you got 45px to add to 250px.

Here is the CSS that will be used in a child theme of Twentytwelve to increase the width of sidebar from 250px to 295px

/* change width of sidebar from 250px to 295px */
/* this leaves 40px between #primary and #secondary */
@media screen and (min-width: 600px) {
	.widget-area {width: 30.7291667%;}
}

Vooov perfect,

Thank you very very much.