Fix ModernDark Card Alignment

Fix cards not showing up properly in ModernDark theme, when more lists are created than will fit on a single screen, inciting a horizontal scrollbar, and then scrolling across trying to open cards.

Due to position being absolute, this then opened the card off-screen

client/components/boards/boardColors.css

@@ -1919,8 +1919,8 @@
 }
 @media screen and (min-width: 801px) {
   .board-color-moderndark .card-details {
-    position: absolute;
-    top: 30px;
+    position: fixed;
+    top: 97px;
     left: calc(50% - 384px);
     width: 768px;
     max-height: calc(100% - 60px);