diff --git a/addons/mail/static/src/attachments/attachment_view.scss b/addons/mail/static/src/attachments/attachment_view.scss
index 259eca6f276..6d88167eab7 100644
--- a/addons/mail/static/src/attachments/attachment_view.scss
+++ b/addons/mail/static/src/attachments/attachment_view.scss
@@ -4,7 +4,6 @@
         flex: 1 0 auto;
         overflow: hidden;
         width: $o-mail-Chatter-minWidth;
-        border-left: 1px solid map-get($grays, '400');
 
         > .o-mail-Attachment {
             position: relative;
diff --git a/addons/mail/static/src/views/form/form_compiler.js b/addons/mail/static/src/views/form/form_compiler.js
index 70b648ea0fc..7accd14c205 100644
--- a/addons/mail/static/src/views/form/form_compiler.js
+++ b/addons/mail/static/src/views/form/form_compiler.js
@@ -112,7 +112,7 @@ patch(FormCompiler.prototype, "mail", {
                 "t-if": `__comp__.hasFileViewer() and __comp__.uiService.size >= ${SIZES.XXL}`,
             });
             const sheetBgChatterContainerHookXml = chatterContainerHookXml.cloneNode(true);
-            sheetBgChatterContainerHookXml.classList.add("o-isInFormSheetBg");
+            sheetBgChatterContainerHookXml.classList.add("o-isInFormSheetBg", "w-auto");
             setAttributes(sheetBgChatterContainerHookXml, {
                 "t-if": `__comp__.hasFileViewer() and __comp__.uiService.size >= ${SIZES.XXL}`,
             });
diff --git a/addons/mail/static/src/views/form/form_renderer.scss b/addons/mail/static/src/views/form/form_renderer.scss
index c68de30488e..c26f76e736f 100644
--- a/addons/mail/static/src/views/form/form_renderer.scss
+++ b/addons/mail/static/src/views/form/form_renderer.scss
@@ -26,8 +26,8 @@
     }
 
     &.o-isInFormSheetBg {
-        background-color: $white;
-        border-top: 1px solid $border-color;
+        margin-left: calc(var(--formView-sheetBg-padding-x) * -1);
+        margin-right: calc(var(--formView-sheetBg-padding-x) * -1);
     }
 
     &:not(.o-aside):not(.o-full-width) .o-mail-Chatter {