session-android/messenger/res/drawable/default_bottom_sheet_background.xml

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <solid android:color="?attr/dialog_background_color" />

    <corners
        android:topLeftRadius="@dimen/dialog_corner_radius"
        android:topRightRadius="@dimen/dialog_corner_radius" />

<!--    <stroke android:width="@dimen/border_thickness" android:color="@color/dialog_border" />-->
</shape>