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/document-viewer/docx/index.less

@@ -13,7 +13,8 @@
   :global(.document-container) {
     padding: 30px;
     width: 700px;
-    background: white;
+    background: rgba(255, 255, 255, 0.1);
+
     margin: auto;
   }