Hello Android - UDACITY business card app

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#2196F3"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/img_udacity_big"
        android:layout_width="match_parent"
        android:layout_height="190dp"
        android:scaleType="centerCrop"
        android:src="@drawable/udacity_wall" />

    <ImageView
        android:id="@+id/img_udacity_wallmono"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:layout_marginStart="10dp"
        android:layout_marginTop="10dp"
        android:scaleType="centerCrop"
        android:src="@drawable/udacity_icon" />

    <TextView
        android:id="@+id/tv_tagline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="105dp"
        android:layout_marginTop="72dp"
        android:textColor="#1976D2"
        android:text="@string/tv_tagline" />

    <TextView
        android:id="@+id/tv_tagline2"
        android:background="#000000"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/img_udacity_big"
        android:layout_marginTop="15dp"
        android:paddingEnd="50dp"
        android:paddingTop="20dp"
        android:paddingBottom="20dp"
        android:textAlignment="textEnd"
        android:textStyle="bold"
        android:textSize="20sp"
        android:fontFamily="sans-serif-condensed"
        android:textColor="#FFFFFF"
        android:text="@string/tv_tagline2" />

    <ImageView
        android:id="@+id/img_udacitymono2"
        android:src="@drawable/udacity_mono1"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:layout_below="@id/img_udacity_big"
        android:layout_marginTop="22dp"
        android:layout_marginLeft="20dp" />

    <Button
        android:id="@+id/button_udacity"
        android:background="@drawable/button_round"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/tv_tagline2"
        android:layout_marginTop="10dp"
        android:padding="15dp"
        android:textSize="16sp"
        android:fontFamily="monospace"
        android:textColor="#000000"
        android:onClick="toWiki"
        android:text="@string/btn_udacity" />

    <Button
        android:id="@+id/button_address"
        android:background="@drawable/button_round_2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/button_udacity"
        android:layout_marginTop="10dp"
        android:padding="15dp"
        android:textSize="16sp"
        android:fontFamily="monospace"
        android:textColorLink="#000000"
        android:autoLink="map"
        android:text="@string/btn_address" />

    <Button
        android:id="@+id/button_phone"
        android:background="@drawable/button_round"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/button_address"
        android:layout_marginTop="10dp"
        android:padding="15dp"
        android:textSize="16sp"
        android:fontFamily="monospace"
        android:textColorLink="#000000"
        android:autoLink="phone"
        android:text="@string/btn_phone" />

    <View
        android:id="@+id/divider"
        android:layout_width="300dp"
        android:layout_height="1dp"
        android:layout_below="@id/button_phone"
        android:layout_marginTop="20dp"
        android:layout_centerHorizontal="true"
        android:background="@drawable/separator" />

    <TextView
        android:id="@+id/tv_link"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_below="@id/divider"
        android:layout_marginTop="10dp"
        android:fontFamily="sans-serif-condensed"
        android:gravity="center"
        android:padding="5dp"
        android:textColor="#000000"
        android:textSize="15sp"
        android:textStyle="italic"
        android:onClick="toWeb"
        android:text="@string/tv_weblink" />

    <ImageView
        android:id="@+id/img_weblink"
        android:src="@drawable/img_web"
        android:layout_width="26dp"
        android:layout_height="29dp"
        android:layout_below="@id/divider"
        android:layout_marginTop="10dp"
        android:layout_toStartOf="@id/tv_link"
        android:padding="2dp"
        android:onClick="toWeb" />

    <TextView
        android:id="@+id/tv_email"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_below="@id/tv_link"
        android:layout_marginTop="5dp"
        android:gravity="center"
        android:textColorLink="#000000"
        android:textStyle="italic"
        android:fontFamily="sans-serif-condensed"
        android:textSize="15sp"
        android:autoLink="email"
        android:clickable="true"
        android:text="@string/text_email" />

    <ImageView
        android:id="@+id/img_email"
        android:src="@drawable/ic_email_black"
        android:layout_width="23dp"
        android:layout_height="26dp"
        android:layout_below="@id/img_weblink"
        android:layout_marginEnd="3dp"
        android:layout_toStartOf="@id/tv_email"
        android:padding="2dp"
        android:onClick="toGmail" />

</RelativeLayout>

Screenshot of the app: