Add fallback for IE8 styles

src/components/accordion/_accordion.scss

@@ -125,7 +125,9 @@
     }
 
     .govuk-accordion__section--expanded .govuk-accordion__section-header--focused {
-      border-top-color: $govuk-focus-colour;
+      @include govuk-not-ie8 {
+        border-top-color: $govuk-focus-colour;
+      }
       // When colours are overridden, for example when users have a dark mode,
       // backgrounds and box-shadows disappear, so we need to ensure there's a
       // transparent outline which will be set to a visible colour.
@@ -159,6 +161,13 @@
         }
       }
 
+      @include govuk-if-ie8 {
+        &:focus {
+          color: $govuk-text-colour;
+          background: $govuk-focus-colour;
+        }
+      }
+
       // Remove default button focus outline in Firefox
       &::-moz-focus-inner {
         padding: 0;