Input With Unknown Min Width

I’m working on creating an input that fits to the width of its content. I have a text and an input grouped together in an align-to-parent group. The group fits to width, the text fits to width, and the input is set to 100% width of the group.

This generally works, except the input will not collapse past ~150px. I have not set a minimum width so I’m not sure why the width of the input won’t collapse past this point.