session-android/res/layout/media_overview_item.xml

<?xml version="1.0" encoding="utf-8"?>
<org.thoughtcrime.securesms.components.SquareLinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <org.thoughtcrime.securesms.components.ThumbnailView
            android:id="@+id/image"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:scaleType="centerCrop"
            android:background="#11ffffff"
            android:contentDescription="@string/media_preview_activity__image_content_description" />

</org.thoughtcrime.securesms.components.SquareLinearLayout>