Center events/news cards on front page

News+Event cards were aligned left-hand on medium-width screens.

So I centered them. @frust45 okay like this?

_sass/common/_cards.scss

 .flex-cards {
     display: flex;
     flex-flow: wrap;
-    justify-content: flex-start;
+    justify-content: center;
 
     margin-top: 0rem;
     margin-bottom: 0rem;