 
 
 AlertDialog.Builder builder = new AlertDialog.Builder(mActivity,
            R.style.MyAlertDialogStyle);
    builder.setTitle(mActivity.getResources().getString(R.string.app_name));
    builder.setCancelable(false);
    builder.setMessage(str_message);
    builder.setPositiveButton(str_btn1,
            new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    if (listener != null) {
                        listener.onClick(null);
                    }
                }
            });
    if (str_btn2 != null) {
        builder.setNegativeButton(str_btn2,
                new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface,
                                        int i) {
                        if (listener2 != null) {
                            listener2.onClick(null);
                        }
                    }
                });
    }
    builder.show();
Edit : Please see the image above. You will get the output like this. Simply create a dialog style
Dialog Style in styles.xml
    <style name="MyAlertDialogStyle" parent="Theme.AppCompat.Light.Dialog.Alert"> <!-- Used for the buttons -->
    <item name="android:textStyle">bold</item>
    <item name="colorAccent">@android:color/holo_blue_bright</item>
    <!-- Used for the title and text -->
    <item name="android:textColorPrimary">@android:color/black</item>
    <!-- Used for the background -->
    <item name="android:background">@android:color/white</item>
</style>