Fix: visible issue in touch device (#3491)

build/scss/_mixins.scss

@@ -11,4 +11,5 @@
 @import "mixins/backgrounds";
 @import "mixins/direct-chat";
 @import "mixins/toasts";
+@import "mixins/touch-support";
 @import "mixins/miscellaneous";

build/scss/mixins/_touch-support.scss

@@ -0,0 +1,11 @@
+//
+// Mixins: Touch Support
+//
+
+@mixin on-touch-device {
+  @media (hover: none) and (pointer: coarse) {
+    @content;
+  }
+}
+
+//

build/scss/pages/_iframe.scss

@@ -37,6 +37,10 @@ body.iframe-mode-fullscreen {
         animation-fill-mode: both;
         visibility: visible;
       }
+
+      @include on-touch-device () {
+        visibility: visible;
+      }
     }
     .navbar-nav {
       overflow-y: auto;
@@ -55,6 +59,10 @@ body.iframe-mode-fullscreen {
             animation-duration: $transition-speed;
             animation-fill-mode: both;
             visibility: visible;
+
+            @include on-touch-device () {
+              visibility: visible;
+            }
           }
         }
       }