UX: Fix slider appearance (#170)

UX: Fix slider appearance (#170)

diff --git a/assets/stylesheets/common/discourse-calendar.scss b/assets/stylesheets/common/discourse-calendar.scss
index 3ec64bf..4e35be9 100644
--- a/assets/stylesheets/common/discourse-calendar.scss
+++ b/assets/stylesheets/common/discourse-calendar.scss
@@ -273,11 +273,12 @@ a.holiday {
     height: 2px;
     top: 50%;
     width: 100%;
-    z-index: -1;
   }
 }
 
 .group-timezones-slider {
+  position: relative;
+  z-index: 1; // need a positive z-index to appear above the ::before
   display: flex;
   width: 120px;
   padding: 0.25em;

GitHub sha: b90f73ec1c2097f1a2fd14c089b52a558c29fce5

This commit appears in #170 which was approved by pmusaraj. It was merged by awesomerobot.