style(背景图组件): 优化并删除冗余代码

src/components/BackgroundLayer.vue

@@ -26,26 +26,13 @@ const props = defineProps({
   // 层级样式
   layerStyle: {
     type: Object,
-    default: () => ({
-      width: '100vw',
-      minHeight: '100vh',
-      position: 'absolute',
-      top: '0',
-      left: '0',
-      zIndex: 0,
-      pointerEvents: 'none',
-    }),
+    default: () => ({}),
   },
 
   // 图片样式
   imageStyle: {
     type: Object,
-    default: () => ({
-      width: '100vw',
-      objectFit: 'cover',
-      objectPosition: 'center top',
-      display: 'block',
-    }),
+    default: () => ({}),
   },
 
   // 图片类名