Fix/limit scoping of accordion styles

These styles (particularly the box-shadow) were being incorrectly
applied to all child elements, which caused the inner Comments accordion
to be styled incorrectly. I failed to catch this when it was introduced
in elastic#178023.

x-pack/solutions/security/plugins/security_solution/public/exceptions/components/exceptions_list_card/index.tsx

@@ -102,7 +102,7 @@ export const ExceptionsListCard = memo<ExceptionsListCardProps>(
           flex: 1 1 auto;
           cursor: pointer;
         }
-        .euiAccordion__triggerWrapper {
+        > .euiAccordion__triggerWrapper {
           z-index: 100;
           position: relative;
           border-radius: ${euiTheme.border.radius.medium};