refactor(components): [overlay] use useNamespace (#5723)

packages/components/overlay/src/overlay.ts

@@ -1,6 +1,6 @@
 import { createVNode, defineComponent, renderSlot, h } from 'vue'
 import { PatchFlags } from '@element-plus/utils/vnode'
-import { useSameTarget } from '@element-plus/hooks'
+import { useNamespace, useSameTarget } from '@element-plus/hooks'
 import { buildProps, definePropType } from '@element-plus/utils/props'
 
 import type { ExtractPropTypes, CSSProperties } from 'vue'
@@ -40,6 +40,8 @@ export default defineComponent({
   emits: overlayEmits,
 
   setup(props, { slots, emit }) {
+    const ns = useNamespace('overlay')
+
     const onMaskClick = (e: MouseEvent) => {
       emit('click', e)
     }
@@ -56,7 +58,7 @@ export default defineComponent({
         ? createVNode(
             'div',
             {
-              class: ['el-overlay', props.overlayClass],
+              class: [ns.b(), props.overlayClass],
               style: {
                 zIndex: props.zIndex,
               },