This Scrippy stationery will automatically expand ALL the containers proportionally to fit the size of the viewer's preview pane window.

All containers were positioned 30 pixels from the top and the height of each was set at 200 pixels. 

The center container has its Left and Right edges set at 175 pixels each.  That gives me room for a container on each side that is less than 175 pixels in width.  So I'll make each side container 150 pixels wide.

The left container was created 150 pixels wide and set 15 pixels from the left.  150 + 15 = 165 pixels, which still fits into the 175 pixel space to the left of the center container.

The right container was created 150 pixels wide and set 15 pixels from the right.  150 + 15 = 165 pixels, which still fits into the 175 pixel space to the right of the center container.

To test how this works, reduce the width of your browser window.  If you're currently viewing it full screen, click the center restore button at the top, right hand corner of your browser, next to the X.   Now you can mouse over the left side of the browser window until you get a double pointed arrow, and then drag the left side of the browser window to the right.  As you do, you'll see that the containers change their sizes.

If you keep dragging the left side of the window to the right, you'll reach a point where Scrippy will stop resizing the containers and it will provide the viewer with a scroll bar at the bottom for viewing.  This point is reached when the preview pane becomes smaller than the total width of your graphics and the margins you've set in the control panel on the left.