res_color_btn_flat_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_enabled="false"
          android:color="@color/flat_disabled_text"/>
    <item android:color="@color/flat_normal_text"/>
</selector>

res_drawable-v21_btn_flat_normal.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
 
    <solid android:color="@android:color/white" />
    <corners android:radius="@dimen/btn_flat_corner_radius" />
</shape>

res_drawable-v21_btn_flat_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<ripple xmlns:android="http://schemas.android.com/apk/res/android"
        android:color="@color/flat_pressed">
    <item
            android:id="@android:id/mask"
            android:drawable="@drawable/btn_flat_normal"/>
</ripple>

res_drawable_btn_flat_pressed.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
    <solid android:color="@color/flat_pressed" />
    <corners android:radius="@dimen/btn_flat_corner_radius" />
</shape>

res_drawable_btn_flat_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android"
          android:exitFadeDuration="@android:integer/config_mediumAnimTime"
          android:enterFadeDuration="@android:integer/config_mediumAnimTime">
 
    <item android:drawable="@drawable/btn_flat_pressed" android:state_pressed="true" />
    <item android:drawable="@android:color/transparent" />
</selector>

res_layout_somewhere.xml

<Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        style="@style/AppCompat.Button.Flat"
        android:text="Button"/>

res_values_colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="flat_pressed">#66999999</color>
    <color name="flat_disabled_text">#40000000</color>
    <color name="flat_normal_text">#000000</color>
</resources>

res_values_dimen.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen name="btn_flat_corner_radius">1dp</dimen>
    <dimen name="btn_flat_min_width">88dp</dimen>
    <dimen name="btn_flat_min_height">36dp</dimen>
    <dimen name="btn_flat_padding">8dp</dimen>
    <dimen name="btn_flat_margin">4dp</dimen>
</resources>

res_values_styles.xml

<resources>
 
    <style name="AppCompat.Button.Flat.Common" parent="Base.TextAppearance.AppCompat.Button">
        <item name="android:background">@drawable/btn_flat_selector</item>
        <item name="android:minWidth">@dimen/btn_flat_min_width</item>
        <item name="android:minHeight">@dimen/btn_flat_min_height</item>
        <item name="android:textColor">@color/btn_flat_selector</item>
        <item name="android:textAllCaps">true</item>
        <item name="android:textStyle">bold</item>
        <item name="android:paddingLeft">@dimen/btn_flat_padding</item>
        <item name="android:paddingRight">@dimen/btn_flat_padding</item>
        <item name="android:layout_marginLeft">@dimen/btn_flat_margin</item>
        <item name="android:layout_marginRight">@dimen/btn_flat_margin</item>
    </style>
 
</resources>