Use min() for modal top position

[benjaminleonard]

On taller screens the modal seems like it comes down a bit far (at 50%). Also, if the height of the modal changes (with some dynamic content) at all the position of say an input will no longer be where it was previously.

We could use min() – that way we make it a fixed position at the top and then have it snap to 50% if the modal moves to a threshold.