ReaderforSelfoss/app/src/main/res/layout/activity_reader.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    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"
    tools:context="apps.amine.bou.readerforselfoss.ReaderActivity"
    android:background="?android:attr/windowBackground">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="200dp"
        android:scaleType="centerCrop"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        />

    <TextView
        android:id="@+id/source"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="8dp"
        android:textAppearance="@style/TextAppearance.AppCompat.Small"
        android:textSize="12sp"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView" />

    <TextView
        android:id="@+id/title"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="6dp"
        android:textAppearance="@style/TextAppearance.AppCompat.Headline"
        android:textStyle="bold"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/source" />

    <org.sufficientlysecure.htmltextview.HtmlTextView
        android:id="@+id/content"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="24dp"
        android:paddingBottom="48dp"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/title"
        tools:text="Some text @android:string/fingerprint_icon_content_description" />

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="35dp"
        android:layout_marginBottom="0dp"
        android:layout_marginEnd="0dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="16dp"
        android:background="#BBBBBB"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/content"
        app:layout_constraintVertical_bias="1.0">

        <ImageButton
            android:id="@+id/browserBtn"
            android:layout_width="35dp"
            android:layout_height="35dp"
            android:layout_centerVertical="true"
            android:layout_marginEnd="16dp"
            android:layout_marginRight="16dp"
            android:layout_toLeftOf="@+id/shareBtn"
            android:layout_toStartOf="@+id/shareBtn"
            android:adjustViewBounds="true"
            android:background="@android:color/transparent"
            android:elevation="5dp"
            android:padding="4dp"
            android:scaleType="centerCrop"
            android:src="@drawable/ic_open_in_browser_black_24dp"
            android:tint="@android:color/black"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toStartOf="@+id/shareBtn"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <ImageButton
            android:id="@+id/shareBtn"
            android:layout_width="35dp"
            android:layout_height="35dp"
            android:adjustViewBounds="true"
            android:background="@android:color/transparent"
            android:elevation="5dp"
            android:padding="4dp"
            android:scaleType="centerCrop"
            android:src="@drawable/ic_share_black_24dp"
            android:tint="@android:color/black"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/browserBtn"
            app:layout_constraintTop_toTopOf="parent" />

    </android.support.constraint.ConstraintLayout>

</android.support.constraint.ConstraintLayout>