style: remove unnused classes

data/resources/style.css

-.video {
-  opacity: 0;
-}
-.video.playing {
-  opacity: 1;
-  transition-property: opacity;
-  transition-duration: 250ms;
-  transition-timing-function: ease-in-out;
-}
-
-window .titlebar button {
-  min-width: 60px;
-}
-
 /* pages */
 
-@keyframes welcome-bg-move {
-    from { background-position: center 30%, -1400px 0, -600px 0, center 30%; }
-    to { background-position: center 30%, 0 0, 0 0, center 30%; }
+@keyframes up-and-down {
+  from {
+    background-position: center 30%, center 30%, center;
   }
 
-@keyframes up-and-down {
-    from { background-position: center 30%, center 30%, center; }
-    to { background-position: center 40%, center 30%, center; }
+  to {
+    background-position: center 40%, center 30%, center;
+  }
 }
 
 @keyframes left-and-right {
-    from { background-position: 40% 30%, center 30%, center; }
-    to { background-position: 60% 30%, center 30%, center; }
+  from {
+    background-position: 40% 30%, center 30%, center;
+  }
+
+  to {
+    background-position: 60% 30%, center 30%, center;
+  }
+}
+
+/* .page:nth-child(2) { background: linear-gradient(to right, #3584e4, #1a5fb4); }  overview */
+.page:nth-child(3) {}
+
+/* customize */
+/* .page:nth-child(4) { background: linear-gradient(to right, #e66100, #c64600); }  workspaces */
+
+.page:nth-child(5) {
+  /* up down */
+  background: url('/org/gnome/Tour/hand-fg.svg'),
+    url('/org/gnome/Tour/updown-bg.svg');
+  background-repeat: no-repeat;
+  background-position: center 30%;
+  animation: up-and-down 2s ease-in-out infinite alternate;
 }
 
-  /* .page:nth-child(2) { background: linear-gradient(to right, #3584e4, #1a5fb4); }  overview */
-  .page:nth-child(3) {  }  /* customize */
-  /* .page:nth-child(4) { background: linear-gradient(to right, #e66100, #c64600); }  workspaces */
-
-  .page:nth-child(5) { /* up down */
-    background: url('/org/gnome/Tour/hand-fg.svg'),
-                url('/org/gnome/Tour/updown-bg.svg');
-    background-repeat: no-repeat;
-    background-position: center 30%;
-    animation: up-and-down 2s ease-in-out infinite alternate;
-    }
-  .page:nth-child(6) {   /* left right */
-    background: url('/org/gnome/Tour/hand-fg.svg'),
-                url('/org/gnome/Tour/leftright-bg.svg');
-    background-repeat: no-repeat;
-    background-position: center 30%;
-    animation: left-and-right 2s ease-in-out infinite alternate;
-    }
+.page:nth-child(6) {
+  /* left right */
+  background: url('/org/gnome/Tour/hand-fg.svg'),
+    url('/org/gnome/Tour/leftright-bg.svg');
+  background-repeat: no-repeat;
+  background-position: center 30%;
+  animation: left-and-right 2s ease-in-out infinite alternate;
+}