change text style

   <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/login_color</item>
        <item name="colorPrimaryDark">@color/login_color</item>
        <item name="colorAccent">@color/login_color</item>
        <item name="android:windowFullscreen">true</item>
        <item name="android:textViewStyle">@style/RobotoTextViewStyle</item>
        <item name="buttonStyle">@style/RobotoButtonStyle</item>
        <item name="android:editTextStyle">@style/RobotoEditTextStyle</item>
    </style>

    <style name="RobotoTextViewStyle" parent="android:Widget.TextView">
        <item name="android:fontFamily">sans-serif-bold</item>
    </style>
    
    
    <style name="RobotoEditTextStyle" parent="android:Widget.EditText">
        <item name="android:fontFamily">sans-serif-bold</item>
    </style>

    <style name="RobotoButtonStyle" parent="android:Widget.Holo.Button">
        <item name="android:fontFamily">sans-serif-bold</item>
    </style>