diff --git a/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection.scss b/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection.scss
deleted file mode 100644
index 0fdda3ec449..00000000000
--- a/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection.scss
+++ /dev/null
@@ -1,18 +0,0 @@
-// ------------------------------------------------------------------
-// Layout
-// ------------------------------------------------------------------
-
-.o_DiscussMobileMailboxSelection {
-    display: flex;
-    flex: 0 0 auto;
-}
-
-.o_DiscussMobileMailboxSelection_button {
-    flex: 1 1 0;
-    padding: map-get($spacers, 2);
-    z-index: 1;
-
-    &.o-active {
-        z-index: 2;
-    }
-}
diff --git a/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection.xml b/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection.xml
index 1b7618e0bc3..dea10c22ec0 100644
--- a/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection.xml
+++ b/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection.xml
@@ -2,9 +2,9 @@
 <templates xml:space="preserve">
 
     <t t-name="mail.DiscussMobileMailboxSelection" owl="1">
-        <div class="o_DiscussMobileMailboxSelection" t-attf-class="{{ className }}" t-ref="root">
+        <div class="o_DiscussMobileMailboxSelection d-flex" t-attf-class="{{ className }}" t-ref="root">
             <t t-foreach="discussView.discuss.orderedMailboxes" t-as="mailbox" t-key="mailbox.localId">
-                <button class="o_DiscussMobileMailboxSelection_button btn btn-secondary"
+                <button class="o_DiscussMobileMailboxSelection_button btn btn-secondary flex-grow-1 p-2"
                     t-att-class="{
                         'active o-active': discussView.discuss.thread === mailbox,
                     }" t-on-click="() => discussView.onClickMobileMailboxSelectionItem(mailbox)" t-att-data-mailbox-local-id="mailbox.localId" type="button"