Improve the webcam picker on small screens

bigbluebutton-html5/imports/ui/components/video-preview/styles.scss

@@ -17,6 +17,10 @@
   display: flex;
 
   width: 30%;
+  @include mq("#{$small-only}") {
+    width: 100%;
+  }
+
   height: 100%;
 
   margin-right: 1.5rem;
@@ -25,6 +29,10 @@
 .content {
   display: flex;
   flex: 3;
+
+  @include mq("#{$small-only}") {
+    flex-direction: column;
+  }
 }
 
 .footer {
@@ -55,6 +63,9 @@
   border-radius: 5px;
   width: 100%;
   height: 8rem;
+  @include mq("#{$small-only}") {
+    height: 100%;
+  }
 }
 
 .row {