Cascader: highlight input when menu clicked (#12341)

Author: ziyoung

packages/cascader/src/main.vue

@@ -30,6 +30,7 @@
       :validate-event="false"
       :size="size"
       :disabled="cascaderDisabled"
+      :class="{ 'is-focus': menuVisible }"
     >
       <template slot="suffix">
         <i

packages/theme-chalk/src/cascader.scss

@@ -14,6 +14,10 @@
     cursor: pointer;
   }
 
+  .el-input.is-focus .el-input__inner {
+    border-color: $--input-focus-border;
+  }
+
   .el-input__icon {
     transition: none;
   }