Custom attributes in styles.xml

above answer is worked for me, I tried a litte change, I declare styleable for a class in resources element.

<declare-styleable name="VerticalView">
    <attr name="textSize" format="dimension" />
    <attr name="textColor" format="color" />
    <attr name="textBold" format="boolean" />
</declare-styleable>

in declare-styleable, the name attribute referenced a class name, so I had a view class call "com.my.package.name.VerticalView", it represented this declare must be use in VerticalView or subclasses of VerticalView. so we can declare style like this :

<resources>
    <style name="verticalViewStyle">
        <item name="android:layout_width">match_parent</item>
        <item name="android:layout_height">36dip</item>

        <item name="textSize">28sp</item>  <!-- not namespace prefix -->
        <item name="textColor">#ff666666</item>
        <item name="textBold">true</item>
    </style>
</resources>

that's why we didn't declare namespace at resources element, it still work.

I figured it out! The answer is to NOT specify the namespace in the style.

<?xml version="1.0" encoding="utf-8" ?>
<resources xmlns:android="http://schemas.android.com/apk/res/android">
    <style name="CustomStyle">
        <item name="android:layout_width">wrap_content</item>
        <item name="android:layout_height">wrap_content</item>

        <item name="custom_attr">value</item> <!-- tee hee -->
    </style>
</resources>

values/styles.xml

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    ...
    <item name="defaultButtonColor">@color/red</item>
    <item name="defaultButtonHeight">@dimen/dp_100</item>
</style>

values/attrs.xml

<resources>
    <attr name="defaultButtonColor" format="reference" />
    <attr name="defaultButtonHeight" format="reference"/>
</resources>

values/colors.xml

<resources>
    <color name="red">#f00</color>
</resources>

values/dimens.xml

<resources>
    <dimen name="dp_100">100dp</dimen>
</resources>

Using

<Button
    android:layout_width="wrap_content"
    android:layout_height="?attr/defaultButtonHeight"
    android:text="Button"
    android:textColor="?attr/defaultButtonColor"
    />

DEMO