Change slider marker for chapters appearance.

Now, the markers are displayed as ticks instead of icons above the slider

src/elements/emby-slider/emby-slider.scss

@@ -255,18 +255,15 @@
 
 .sliderMarker {
     position: absolute;
-    transform: translate3d(0, -100%, 0) rotate(90deg);
-}
-
-.sliderMarker.chapterMarker::before {
-    font-family: 'Material Icons', sans-serif;
-    content: "\e892";
+    width: 2px;
+    height: 0.5em;
+    transform: translate3d(0, 25%, 0);
 }
 
 .sliderMarker.unwatched {
-    color: rgba(255, 255, 255, 0.3);
+    background-color: rgba(255, 255, 255, 0.3);
 }
 
 .sliderMarker.watched {
-    color: #00a4dc;
+    background-color: #00a4dc;
 }