remove black border on buttons

app/assets/javascripts/components/components/video_player.jsx

@@ -23,8 +23,8 @@ const muteStyle = {
   position: 'absolute',
   top: '10px',
   right: '10px',
-  color: 'white',
-  boxShadow: '1px 1px 1px #000',
+  color: white,
+  textShadow: "0px 1px 1px black, 1px 0px 1px black",
   opacity: '0.8',
   zIndex: '5'
 };
@@ -56,8 +56,8 @@ const spoilerButtonStyle = {
   position: 'absolute',
   top: '6px',
   left: '8px',
-  color: 'white',
-  boxShadow: '1px 1px 1px #000',
+  color: white,
+  textShadow: "0px 1px 1px black, 1px 0px 1px black",
   zIndex: '100'
 };