Is that a way to push all two columns further to the right and add a third sidebar to the left with the menu buttons and/or text-widgets? That would be my preferred solution.
There is not a way to do this with CSS only, however, you can push already-existing content around on the page. For example, you could select specific widgets from the right, make some space on the left, and re-position some of the widgets to move them over.
There is a drawback to this solution, and that is that you can only use fixed height widgets on the left or the widgets will overlap each other when their height changes.
Here is an example to show you how a solution like this would work:
.content-sidebar #sidebar-primary,
.layout-default #sidebar-primary {
width: 200px;
}
.content-sidebar #content,
.layout-default #content {
width: 595px;
padding-left: 210px;
}
.contain {
position: relative;
}
#search-2 {
width: 170px;
position: absolute;
top: 45px;
left: 0;
}
#text-12 {
width: 180px;
position: absolute;
top: 165px;
left: 0;
}
Note that this example is very specific to your site. It uses widget ID values "search-2" and "text-12." Each time you add a new widget, it gets a unique ID. You need to add the widget and then look in the page source to find out what it's ID is and then use that in the CSS to move it where you want in the layout.