diff --git a/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.scss b/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.scss
index 8ad191bf533..9761e635308 100644
--- a/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.scss
+++ b/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.scss
@@ -1,10 +1,4 @@
-// ------------------------------------------------------------------
-// Layout
-// ------------------------------------------------------------------
-
 .o_DiscussSidebar {
-    display: flex;
-    flex-flow: column;
     width: $o-mail-chat-sidebar-width;
 
     @include media-breakpoint-up(xl) {
@@ -12,31 +6,9 @@
     }
 }
 
-.o_DiscussSidebar_category {
-    display: flex;
-    flex-flow: column;
-    flex: 0 0 auto;
-}
-
 .o_DiscussSidebar_quickSearch {
     border-radius: 10px;
     margin: 0 $o-mail-discuss-sidebar-scrollbar-width 10px;
     padding: 3px 10px;
-}
-
-.o_DiscussSidebar_separator {
-    width: 100%;
-}
-
-// ------------------------------------------------------------------
-// Style
-// ------------------------------------------------------------------
-
-.o_DiscussSidebar_quickSearch {
-    border: none;
     outline: none;
 }
-
-.o_DiscussSidebar_separator {
-    background-color: $border-color;
-}
diff --git a/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.xml b/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.xml
index cdaa1b72f28..dbd97f9f77c 100644
--- a/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.xml
+++ b/addons/mail/static/src/components/discuss_sidebar/discuss_sidebar.xml
@@ -3,19 +3,19 @@
 
     <t t-name="mail.DiscussSidebar" owl="1">
         <t t-if="discussView">
-            <div name="root" class="o_DiscussSidebar" t-attf-class="{{ className }}" t-ref="root">
+            <div name="root" class="o_DiscussSidebar d-flex flex-column" t-attf-class="{{ className }}" t-ref="root">
                 <div class="d-flex justify-content-center">
                     <button class="o_DiscussSidebar_startAMeetingButton btn btn-primary rounded" title="Start a meeting" t-on-click="discussView.onClickStartAMeetingButton">
                         Start a meeting
                     </button>
                 </div>
-                <hr class="o_DiscussSidebar_separator"/>
-                <div class="o_DiscussSidebar_category o_DiscussSidebar_categoryMailbox">
+                <hr class="o_DiscussSidebar_separator w-100 border-top"/>
+                <div class="o_DiscussSidebar_category o_DiscussSidebar_categoryMailbox d-flex flex-column flex-grow-0">
                     <DiscussSidebarMailbox record="discussView.inboxView"/>
                     <DiscussSidebarMailbox record="discussView.starredView"/>
                     <DiscussSidebarMailbox record="discussView.historyView"/>
                 </div>
-                <hr class="o_DiscussSidebar_separator"/>
+                <hr class="o_DiscussSidebar_separator w-100 border-top"/>
                 <t t-if="messaging.models['Thread'].all(thread => thread.isPinned and thread.model === 'mail.channel').length > 19">
                     <input class="o_DiscussSidebar_quickSearch" t-on-input="discussView.onInputQuickSearch" placeholder="Quick search..." t-ref="quickSearchInput" t-esc="discussView.discuss.sidebarQuickSearchValue"/>
                 </t>