treewide: set css tag flex-wrap to wrap buttons in modal view

treewide: set css tag flex-wrap to wrap buttons in modal view

In CSS, the flex-wrap property is used in a flex container to control
how flex items are laid out when there is not enough space in a single
line.

If a modal is displayed on small screens, the buttons are not wrapped. They
remain on one line. This breaks the layout and does not look good.

Signed-off-by: Florian Eckert <[email protected]>