fix video player various buttons accessibility

common/lib/xmodule/xmodule/css/video/display.scss

@@ -573,7 +573,8 @@ $cool-dark: rgb(79, 89, 93); // UXPL cool dark
               color: rgb(231, 236, 238); // UXPL grayscale-cool x-light
 
               @media (max-width: 1120px) {
-                display: none;
+                  position: absolute;
+                  clip: rect(1px, 1px, 1px, 1px);
               }
             }
 

common/lib/xmodule/xmodule/js/src/video/04_video_full_screen.js

@@ -4,6 +4,8 @@
         var template = [
             '<button class="control add-fullscreen" aria-disabled="false" title="',
             gettext('Fill browser'),
+            '" aria-label="',
+            gettext('Fill browser'),
             '">',
             '<span class="icon fa fa-arrows-alt" aria-hidden="true"></span>',
             '</button>'

common/lib/xmodule/xmodule/js/src/video/07_video_volume_control.js

@@ -46,6 +46,8 @@ function(HtmlUtils) {
                 '<button class="control" aria-disabled="false"',
                 '" aria-expanded="false" title="',
                 '{adjustVideoVolume}',
+                '" aria-label="',
+                '{adjustVideoVolume}',
                 '">',
                 '<span class="icon fa fa-volume-up" aria-hidden="true"></span>',
                 '</button>',

common/lib/xmodule/xmodule/js/src/video/08_video_speed_control.js

@@ -41,9 +41,9 @@
             '<span>',
             '<span class="icon fa fa-caret-right" aria-hidden="true"></span>',
             '</span>',
-            '<span class="label" aria-hidden="true">',
+            '<span class="label">',
             gettext('Speed'),
-            '</span>',
+            ' </span>',
             '<span class="value"></span>',
             '</button>',
             '<ol class="video-speeds menu"></ol>',