...
Popups should always remain horizontally and vertically centred, regardless of the screen dimensions.
On large screens popups should remain at their default size.
The left and right internal padding for all popups should reduce to 24px at the same 900px breakpoint.
Where the screen dimensions are smaller than the popup’s height or width, the popup size should be adjusted. A minimum margin of 24px should persist around all four sides of the popup.
When the popup size is reduced and the full content cannot be displayed:
the header text will be truncated with an ellipsis. The full header will be shown in a tooltip on hover.
the elements within the main content area will respond, following their own responsive guidelines. A vertical scrollbar may be added where necessary.
...