Add styling and display css for the children

Author: musale

packages/mgt-components/src/components/mgt-file-list/mgt-file-list.scss

@@ -58,6 +58,25 @@ $progress-ring-size: var(--progress-ring-size, 24px);
     flex-direction: column;
     list-style: none;
 
+    .file-list-children {
+      &-show {
+        display: block;
+        margin-inline-start: calc($file-list-margin + 32px);
+
+        ul {
+          list-style: none;
+
+          li {
+            padding: 8px 0px;
+          }
+        }
+      }
+
+      &-hide {
+        display: none;
+      }
+    }
+
     .file-item {
       cursor: pointer;
       border-radius: var(--file-border-radius);
@@ -77,6 +96,10 @@ $progress-ring-size: var(--progress-ring-size, 24px);
         --file-border-radius: 2px;
         --file-background-color: var(--file-item-background-color, var(--neutral-layer-1));
       }
+
+      .file-list-children {
+        background-color: beige;
+      }
     }
   }