Alerts

From Google material design documentation

Alerts are urgent interruptions, requiring acknowledgement, that inform the user about a situation.

How to add?

I. In your build.gradle add latest appcompat library.

dependencies {  
    compile 'com.android.support:appcompat-v7:X.X.X' // where X.X.X version
}

II. Make your activity extend android.support.v7.app.AppCompatActivity.

public class MainActivity extends AppCompatActivity {  
    ...
}

III. To create your dialog use android.support.v7.app.AlertDialog.Builder.

private void showLocationDialog() {  
    AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
    builder.setTitle(getString(R.string.dialog_title));
    builder.setMessage(getString(R.string.dialog_message));

    String positiveText = getString(android.R.string.ok);
    builder.setPositiveButton(positiveText,
            new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            // positive button logic
        }
    });

    String negativeText = getString(android.R.string.cancel);
    builder.setNegativeButton(negativeText,
            new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            // negative button logic
        }
    });

    AlertDialog dialog = builder.create();
    // display dialog
    dialog.show();
}

How to style?

I. Declare custom drawable.xml for dialog background.

<?xml version="1.0" encoding="utf-8"?>  
<!-- From: support/v7/appcompat/res/drawable/abc_dialog_material_background_light.xml -->  
<inset xmlns:android="http://schemas.android.com/apk/res/android"  
    android:insetLeft="16dp"
    android:insetTop="16dp"
    android:insetRight="16dp"
    android:insetBottom="16dp">

    <shape android:shape="rectangle">
        <corners android:radius="2dp" />
        <solid android:color="@color/indigo" />
    </shape>

</inset>  

II. Declare custom styles in your styles.xml file.

<style name="MyDialogTheme" parent="Theme.AppCompat.Light.Dialog.Alert">  
    <!--buttons color-->
    <item name="colorAccent">@color/pink</item>
    <!--title and message color-->
    <item name="android:textColorPrimary">@android:color/white</item>
    <!--dialog background-->
    <item name="android:windowBackground">@drawable/background_dialog</item>
</style>  

III. Create your dialog and use style as parameter in AlertDialog.Builder.

AlertDialog.Builder builder =  
        new AlertDialog.Builder(this, R.style.MyDialogTheme);
...
AlertDialog dialog = builder.create();  
// display dialog
dialog.show();  

You can also style dialog in your activity theme via alertDialogTheme attribute.