Custom Control Design-Time Resize?

I have a simple composite control that contains a Label
with a textbox immediately below the label.

At design time, when the developer resizes the control, I
would like to resize the contained Textbox so that its
width is slightly less than the width of the control.

Anyone know how to do this?

When placing the textbox on your usercontrol, place it with the right distance to the borders.
Then set the Anchor property to Top,Left,Right.
Now the textbox will automatically keep the distance to the borders.