Set story viewer background exit fade duration to 100ms.

app/src/main/java/org/thoughtcrime/securesms/stories/viewer/StoryViewerActivity.kt

@@ -3,6 +3,7 @@ package org.thoughtcrime.securesms.stories.viewer
 import android.content.Context
 import android.content.Intent
 import android.net.Uri
+import android.os.Build
 import android.os.Bundle
 import androidx.appcompat.app.AppCompatDelegate
 import org.thoughtcrime.securesms.PassphraseRequiredActivity
@@ -45,6 +46,12 @@ class StoryViewerActivity : PassphraseRequiredActivity(), VoiceNoteMediaControll
     }
   }
 
+  override fun onEnterAnimationComplete() {
+    if (Build.VERSION.SDK_INT >= 21) {
+      window.transitionBackgroundFadeDuration = 100
+    }
+  }
+
   companion object {
     private const val ARG_START_RECIPIENT_ID = "start.recipient.id"
     private const val ARG_START_STORY_ID = "start.story.id"