MM-56975 UI Incremental Refinements (#26407)

* updated styles to include rounded corners and updated backgrounds/containers

* updated snapshots

* removed background from app bar top

* removed top padding from lhs

* updated name of container to better match the grid name in css

* fixed lint issue with css

* update snapshot

* adjusted padding/margin

* use radius variables

* remove margin and border radius from plabooks for now

* fixed tasklist

* minor tweaks to menus

* add global border variables and use in key places

* fixed grid issues with login page and backstage

* use border variable

* adjust padding in global header

* fixed type issues

* tweaks to spacing

* fixed margin issue on backstage

* fixed padding on global header

* minor tweaks to header and apps bar

* removed background from apps bar

* updates to header and app bar and team icon

* updated more borders and radii to use variables

* fixed style lint issue

* adjust letter spacing on category labels

* fix lint issue

* fixed position of popover

* address UX feedback

webapp/platform/components/src/generic_modal/generic_modal.scss

@@ -23,13 +23,13 @@
         padding: 0;
 
         &.divider {
-            border-top: 1px solid rgba(var(--center-channel-color-rgb), 0.08);
+            border-top: var(--border-light);
         }
 
         .form-control {
             height: 40px;
             box-sizing: border-box;
-            border: 1px solid rgba(var(--center-channel-color-rgb), 0.16);
+            border: var(--border-default);
             border-radius: 4px;
 
             &:focus {
@@ -96,7 +96,7 @@
                 border: 1px solid rgba(var(--dnd-indicator-rgb), 0.16);
                 margin-bottom: 24px;
                 background: rgba(var(--dnd-indicator-rgb), 0.08);
-                border-radius: 4px;
+                border-radius: var(--radius-s);
 
                 span {
                     color: var(--center-channel-color);