Grid: Add button styling fix (#10978)

* Add missing focus styling

* Ensure add button is perfectly rounded and remove unused / uneeded CSS.

* Remove redundant border-color property

* Revert removal of unused css

Co-authored-by: BatJan <jaskov@gmail.com>
Co-authored-by: Jan Skovgaard Olsen <jso@co3.dk>
(cherry picked from commit 31ecc146d1)

src/Umbraco.Web.UI.Client/src/less/components/umb-grid.less

@@ -565,12 +565,11 @@
 // ICONS
 // -------------------------
 .umb-grid .iconBox {
-    padding: 4px 6px;
-    display: inline-block;
-    cursor: pointer;
+    padding: 6px;
+    display: flex;
     border-radius: 200px;
     border: 1px solid @ui-action-discreet-border;
-    margin: 2px;
+    margin: 0 auto;
 
     &:hover, &:hover * {
         background: @ui-action-discreet-type-hover !important;
@@ -599,8 +598,6 @@
     -webkit-appearance: none;
     background-image: linear-gradient(to bottom,@gray-9,@gray-7);
     background-repeat: repeat-x;
-    zoom: 1;
-    border-color: @gray-7 @gray-7 @gray-6;
     border-color: rgba(0,0,0,0.1) rgba(0,0,0,0.1) rgba(0,0,0,0.25);
     box-shadow: inset 0 2px 4px rgba(0,0,0,0.15),0 1px 2px rgba(0,0,0,0.05);
     border-radius: 3px;