How to set dynamic width on components in Application Studio?

In the application studio does anyone know how to set the width of components to be the same as the width of the container or a scalable percent? In the image below you can see the print button is full width but the inventory quantity box isn’t. When clicking on the box and layout, you only get options for alignment and width. However it seems width only takes a number of pixels. I wouldn’t want to set it to a specific amount of pixels as I don’t know the users screen resolution. Thanks.