feat: placeholder in a new chat

src/assets/styles/components/_chat.scss

@@ -19,6 +19,8 @@ $chat-avatar-size: 40px;
 
 $scroll-bar-width: 4px;
 
+$placeholder-height: 248px;
+
 .a-chat {
   display: block;
   text-decoration: none;
@@ -53,6 +55,7 @@ $scroll-bar-width: 4px;
     left: 0;
     overflow-y: scroll;
     overflow-x: hidden;
+    scrollbar-gutter: stable both-edges;
     width: 100%;
     height: 100%;
     padding: 16px 16px 0 16px;