diff --git a/addons/im_livechat/static/src/legacy/public_livechat.scss b/addons/im_livechat/static/src/legacy/public_livechat.scss
index af8f95c32e6..ccc552ff7e9 100644
--- a/addons/im_livechat/static/src/legacy/public_livechat.scss
+++ b/addons/im_livechat/static/src/legacy/public_livechat.scss
@@ -687,6 +687,7 @@ $o-mail-thread-window-zindex: $zindex-modal + 1 !default;
 
 .o_PublicLivechatMessage_background {
     position: absolute;
+    z-index: -1;
     left: 0;
     top: 0;
     width: 100%;