feat: pref message send box style (#335)

Co-authored-by: brzhang <hoollyzhang@tencent.com>

frontend/src/components/ChatInterface.css

@@ -53,7 +53,7 @@
 }
 
 .input-container {
-  width: 98%;
+  width: 100%;
   display: flex;
   align-items: center;
   background-color: #3e3e3e;