diff --git a/app/assets/stylesheets/components/broadcast-message.scss b/app/assets/stylesheets/components/broadcast-message.scss
index d9e51f85f..672ce5207 100644
--- a/app/assets/stylesheets/components/broadcast-message.scss
+++ b/app/assets/stylesheets/components/broadcast-message.scss
@@ -6,6 +6,7 @@
     max-width: 464px;
     box-sizing: border-box;
     padding: govuk-spacing(9) govuk-spacing(3) govuk-spacing(3) govuk-spacing(3);
+    border: solid 1px transparent; // to show it's area in high contrast mode
     background: $panel-colour;
     box-shadow: inset 0 -1px 0 0 rgba(0, 0, 0, 0.05);
     border-radius: 5px;
@@ -18,10 +19,11 @@
   &-heading {
     display: block;
     position: absolute;
-    top: 0;
-    left: 0;
+    top: -1px;
+    left: -1px;
     padding: govuk-spacing(2) + 1px govuk-spacing(3) (govuk-spacing(2) - 1px) 46px;
-    width: 100%;
+    border: solid 1px transparent; // to show it's area in high contrast mode
+    width: calc(100% + 2px); // grow to overlap wrapper's border (when combined with top and left)
     box-sizing: border-box;
     font-weight: bold;
     background: $grey-1 file-url('exclamation.svg');