Theme switch support (#3568)

### What problem does this PR solve?
- [x] New Feature (non-breaking change which adds functionality)

---------

Co-authored-by: Yingfeng <yingfeng.zhang@gmail.com>
Co-authored-by: Jin Hai <haijin.chn@gmail.com>

web/src/pages/search/index.less

@@ -15,16 +15,8 @@
     font-size: 14px;
     cursor: pointer;
   }
-
-  // .mainLayout {
-  //   background: transparent;
-  // }
 }
 
-// .transparentSearchSide {
-//   background-color: rgb(251 251 251 / 88%) !important;
-// }
-
 .searchSide {
   position: relative;
   max-width: 400px !important;
@@ -101,10 +93,10 @@
 }
 .answerWrapper {
   margin-top: 16px;
-  background: rgb(232 242 251 / 70%);
+  background: rgba(232 242 251, 1);
   box-shadow: 0 2px 8px 0 rgba(0, 0, 0, 0.08);
   :global(.ant-card-head) {
-    background-color: #e6f4ff;
+    background-color: #e6f4ff23;
   }
   & p {
     margin: 0;

web/src/pages/search/index.tsx

@@ -146,9 +146,9 @@ const SearchPage = () => {
                   ></RetrievalDocuments>
                   <Divider></Divider>
                   <Spin spinning={loading}>
-                    {chunks.length > 0 && (
+                    {chunks?.length > 0 && (
                       <List
-                        dataSource={chunks}
+                        dataSource={chunks || []}
                         className={styles.chunks}
                         renderItem={(item) => (
                           <List.Item>