fix: transition nested example

Author: mostafa-nematpour

src/guide/built-ins/transition-demos/NestedTransitions.vue

@@ -24,6 +24,7 @@ const show = ref(true)
 
 .transition-demo-inner {
   background: #ccc;
+  color: rgb(33, 53, 71);
 }
 
 .nested-enter-active,