diff --git a/addons/mail/static/src/scss/abstract_thread_window.scss b/addons/mail/static/src/scss/abstract_thread_window.scss
index 847eaa5a535..a4ad6d366cc 100644
--- a/addons/mail/static/src/scss/abstract_thread_window.scss
+++ b/addons/mail/static/src/scss/abstract_thread_window.scss
@@ -77,7 +77,7 @@ $o-mail-thread-window-zindex: $zindex-modal + 1 !default;
         -webkit-overflow-scrolling: touch; // smooth scrolling in iOS app (Safari)
 
         .o_thread_typing_notification_bar {
-            @include o-transparent-background-color(0.75, $o-mail-thread-window-bg);
+            background-color: rgba($o-mail-thread-window-bg, 0.75);
         }
 
         .o_thread_date_separator {
diff --git a/addons/mail/static/src/scss/thread.scss b/addons/mail/static/src/scss/thread.scss
index d27680fb404..81f6862ca9f 100644
--- a/addons/mail/static/src/scss/thread.scss
+++ b/addons/mail/static/src/scss/thread.scss
@@ -19,7 +19,7 @@
 
     .o_thread_typing_notification_bar {
         flex: 0, 0, 20px;
-        @include o-transparent-background-color(0.75, white);
+        background-color: rgba($white, 0.75);
         padding: 5px;
         text-align: center;
         color: gray('600');
diff --git a/addons/web/static/src/scss/utils.scss b/addons/web/static/src/scss/utils.scss
index c4fe8c577e8..e63e0c6650f 100644
--- a/addons/web/static/src/scss/utils.scss
+++ b/addons/web/static/src/scss/utils.scss
@@ -48,14 +48,6 @@
     vertical-align: top; // To update display context changed by overflow:hidden
 }
 
-// ------------------------------------------------------------------
-// Transparent background color
-// ------------------------------------------------------------------
-@mixin o-transparent-background-color($alpha: 1, $color: white) {
-    // convert hex to rgba for applying opacity
-    background-color: rgba(red($color), green($color), blue($color), $alpha);
-}
-
 // ------------------------------------------------------------------
 // Hovering effects
 // ------------------------------------------------------------------