Fix jumbotron buttons

Signed-off-by: Eric Poirier <eric.poirier@eclipse-foundation.org>

2021-06/style.css

diff --git a/2021-06/style.css b/2021-06/style.css
index 1106472..a70f842 100644
--- a/2021-06/style.css
+++ b/2021-06/style.css
@@ -92,7 +92,7 @@
 
 
 
-a.btn-primary, a.btn-primary:active {
+a.btn-primary, a.btn-primary:active, a.btn-primary:visited {
   color: #000;
   background-color: #a6c1f2;
   border-color: #a6c1f2;