fix(UI): Improve layout of current time container above hovered seek bar (#8412)

Fixes #8411

Co-authored-by: Loïc Raux <loicraux@gmail.com>

Author: loicraux

ui/less/thumbnails.less

@@ -38,11 +38,15 @@
 }
 
 #shaka-player-ui-time-container {
+  align-items: center;
   background-color: white;
   border: 1px solid black;
   border-radius: 10px;
   box-shadow: 0 8px 8px 0 rgb(0, 0, 0, 50%);
   color: black;
+  display: flex;
+  font-size: 14px;
+  justify-content: center;
   overflow: hidden;
   padding: 1px 7px;
   position: absolute;