Modals are not very mobile-friendly

[ThinkGraphical]

With a fixed width of 500px, the modals aren't very mobile-friendly.

I've resolved this by adding a selector to the 'modal-body'
and overwritten it with width: 90% !important; as a default.
On desktop-viewport added the width: 500px !important;.

Even though it's really easy to do this yourself,
it would be nice if the modals are more mobile-friendly by default.

[yuanyan]

yeah, in my todo list, and pull request welcome!