docs(cdk-experimental/tree): show nav mode checkmark (angular#31743)

Author: wagnermaciel

src/components-examples/cdk-experimental/tree/tree-common.css

@@ -49,6 +49,7 @@
   margin-left: auto;
 }
 
+.example-tree-item[aria-current] .example-selected-icon,
 .example-tree-item[aria-selected='true'] .example-selected-icon {
   visibility: visible;
 }

src/dev-app/cdk-experimental-tree/cdk-tree-demo.css

@@ -1,6 +1,6 @@
 .example-tree-grid {
   display: grid;
-  grid-template-columns: repeat(auto-fit, 100%);
+  grid-template-columns: repeat(auto-fit, minmax(24rem, 1fr));
   gap: 20px;
 }