Changing button style in the whole application

For styling your Button you can use this:

Go to the drawable folder and make an XML (e.g. button.xml) file called "style" which contains the following:

<?xml version="1.0" encoding="utf-8"?> 

<selector xmlns:android="http://schemas.android.com/apk/res/android">  

    <item>
         <shape>
             <gradient android:startColor="#449def" android:endColor="#2f6699" android:angle="270" />
             <stroke   android:width="1px"          android:color="#000000" />  
                <corners android:bottomLeftRadius="0dp"
                android:bottomRightRadius="0dp"
                android:topLeftRadius="8dp"
                android:topRightRadius="8dp"/>       
              <padding  android:left="10dp"  android:top="10dp" android:right="10dp" android:bottom="10dp" />
         </shape>  
   </item> 

</selector>

This is my code, you can make the necessary changes you want

Now call it in your layout XML (mainactivity.xml) like this

android:background="@drawable/button.xml"

Now to change the font color and style you can use the following which comes as part of the styles.xml in the values folder

<style name="buttonStyle" parent="@android:style/Widget.Button.Small">
    <item name="android:textColor">#FFFFFF</item>
    <item name="android:textSize">12sp</item>
    <item name="android:textStyle">bold</item>
</style>

Now call this in the layout XML (mainactivity.xml) like this

  style="@style/buttonStyle"

The final code is:

<Button
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_marginTop="15dp"
 android:text="@string/edit"
 android:id="@+id/btnEdit"
 android:background="@drawable/button.xml"
 style="@style/buttonStyle"
/>

Hope this helps :)

This will change the default button style for the entire app, include alert dialog button. Adjust the style based on yours.

res/values/styles.xml

<resources>

    <!-- Your base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Other styles -->
        <item name="buttonStyle">@style/MyCustomButton</item>
    </style>

    <style name="MyCustomButton" parent="Widget.AppCompat.Button">
        <item name="android:background">@drawable/selector_button</item>
        <item name="android:textColor">@color/buttonText</item>
        <item name="android:textStyle">bold</item>
        <item name="android:paddingLeft">16dp</item>
        <item name="android:paddingRight">16dp</item>
    </style>
</resources>

res/drawable/selector_button.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/button_selected" android:state_pressed="true"/>
    <item android:drawable="@drawable/button_selected" android:state_focused="true"/>
    <item android:drawable="@drawable/button_unselected"/>
</selector>

res/drawable/button_selected.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <corners android:radius="1000dp"/>

    <solid android:color="@color/buttonSelected"/>
</shape>

res/drawable/button_unselected.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <corners android:radius="1000dp"/>

    <solid android:color="@color/buttonUnselected"/>
</shape>