The modules on the dashboard are displayed with top corners as rounded and bottom corners as square. Looking at the css I don't believe this is intentional - especially as the "add module" block has rounded corners top and bottom.

Closer investigation shows that it is caused by

.com_cpanel .card-body {
    padding:0;
}

As soon as you put the padding back to 1rem the corners are back, this css was added by @ciar4n [4.0] Admin UI repaint (#33100) and I assume its a mistake but would prefer @ciar4n to have the opportunity to comment before making a PR.

PS also everything "looks better" to me with the lines not reaching the edges.

screenshot without padding

screenshot with padding