opt: persistent header

Closes #211

ref pilipala

Signed-off-by: bggRGjQaUbCoE <githubaccount56556@proton.me>

lib/common/widgets/custom_sliver_persistent_header_delegate.dart

@@ -19,8 +19,16 @@ class CustomSliverPersistentHeaderDelegate
     //创建child子组件
     //shrinkOffset：child偏移值minExtent~maxExtent
     //overlapsContent：SliverPersistentHeader覆盖其他子组件返回true，否则返回false
-    return ColoredBox(
-      color: bgColor,
+    return DecoratedBox(
+      decoration: BoxDecoration(
+        color: bgColor,
+        boxShadow: [
+          BoxShadow(
+            color: bgColor,
+            offset: const Offset(0, -2),
+          ),
+        ],
+      ),
       child: child,
     );
   }