ui: Small CSS tweaks (#7808)

1. Reinstate top border on in page tabs
2. Keep overflow:hidden just for dom-recycling-tables

ui-v2/app/styles/base/components/tabs/skin.scss

@@ -1,3 +1,7 @@
+%tab-nav {
+  border-top: $decor-border-200;
+  border-color: $gray-200;
+}
 %tab-nav ul {
   list-style-type: none;
 }

ui-v2/app/styles/components/dom-recycling-table/layout.scss

@@ -6,6 +6,9 @@
 }
 %dom-recycling-table tr > * {
   flex: 1 0 auto;
+  /* this means no simple CSS drive tooltips in dom-recycling tables */
+  /* ideally the thing inside the td should be overflow hidden */
+  overflow: hidden;
 }
 %dom-recycling-table tbody {
   /* important required as ember-collection will inline an overflow: visible*/