diff --git a/addons/hr_holidays/static/src/views/calendar/calendar_renderer.scss b/addons/hr_holidays/static/src/views/calendar/calendar_renderer.scss
index e12433e3b07..b6c7e39898b 100644
--- a/addons/hr_holidays/static/src/views/calendar/calendar_renderer.scss
+++ b/addons/hr_holidays/static/src/views/calendar/calendar_renderer.scss
@@ -5,7 +5,8 @@
         .o_calendar_widget {
             @for $size from 1 through length($o-colors) {
                 .hr_stress_day_#{$size - 1}:not(.fc-disabled-day) {
-                    background-color: lighten(nth($o-colors, $size), 25%) !important;
+                    background: nth($o-colors, $size) !important;
+                    opacity: 0.4;
                 }
             }
         }