Apps how to do button with transparent background

[mikewax]

hello i have an app with a big button in the middle of the screen and it looks like this:

and the (coordinator) fragment layout file looks like this:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
androidrientation="vertical">

<View
android:layout_width="match_parent"
android:layout_height="276dp"
android:background="?android:attr/listDivider" />

<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
androidrientation="horizontal"
android:layout_gravity="center_horizontal">

<ImageButton
android:id="@+id/send_btn"
android:layout_width="186dp"
android:layout_height="wrap_content"
app:srcCompat="@drawable/ic_circle"
android:contentDescription="send text to device" />
</LinearLayout>

<TextView
android:id="@+id/receive_text"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:freezesText="true"
android:gravity="bottom"
android:scrollbars="vertical"
android:textAppearance="@Style/TextAppearance.AppCompat.Medium" />

</LinearLayout>

i'm wondering how to get that background on the button to be transparent.