Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Add 'playlistThumbnail' to playlist objects
  Use accurate sub count when available
  Refactor search extractor
  Fix allowed_regions for globally blocked videos
  js: add support to detect alt, meta and control key in keydown handler (iv-org#704)
  Fix playlist_thumbnail extractor
  js: add support for keydown events (iv-org#678)
  Change font family to better native selection (iv-org#679)
  Fix season playlists
  Add prefers-color-scheme support (iv-org#601)

assets/css/default.css

@@ -1,3 +1,10 @@
+html,
+body {
+  font-family: BlinkMacSystemFont, -apple-system, "Segoe UI", Roboto, Oxygen,
+    Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", Helvetica,
+    Arial, sans-serif;
+}
+
 .deleted {
   background-color: rgb(255, 0, 0, 0.5);
 }
@@ -103,6 +110,7 @@ img.thumbnail {
   height: 100%;
   left: 0;
   top: 0;
+  object-fit: cover;
 }
 
 .length {
@@ -113,7 +121,6 @@ img.thumbnail {
   border-radius: 2px;
   padding: 2px;
   font-size: 16px;
-  font-family: sans-serif;
   right: 0.25em;
   bottom: -0.75em;
 }
@@ -126,7 +133,6 @@ img.thumbnail {
   border-radius: 2px;
   padding: 4px 8px 4px 8px;
   font-size: 16px;
-  font-family: sans-serif;
   left: 0.2em;
   top: -0.7em;
 }
@@ -439,8 +445,8 @@ video.video-js {
 }
 
 .video-js.player-style-youtube .vjs-control-bar {
-   display: flex;
-   flex-direction: row;
+  display: flex;
+  flex-direction: row;
 }
 .video-js.player-style-youtube .vjs-big-play-button {
   /*
@@ -449,6 +455,6 @@ video.video-js {
   */
   top: 50%;
   left: 50%;
-  margin-top: -.81666em;
+  margin-top: -0.81666em;
   margin-left: -1.5em;
 }