Thanks for your reply. Now I get it (Owl and Reply helped). We have themes that define the colors used by the attributes. We’ve styles to reuse view attributes and if we specify some colors we should use ?attr. Finally we have custom attr when the MDC ones aren’t enough.

That said,

Style:

<style name="App.WidgetStyle.Button" parent="Widget.MaterialComponents.Button.TextButton">
 ...
 <item name="android:textSize">14sp</item>
 <item name="android:textAllCaps">true</item>
 <item name="android:textAlignment">center</item>
 <item name="android:textColor">@color/selector_for_btn_text</item>
 <item name="backgroundTint">@color/selector_for_btn</item>
 <item name="android:fontFamily">@font/open_sans_bold</item>
 <item name="rippleColor">?attr/rippleColor</item>
 <item name="iconTint">?attr/viewsIconTint</item>
</style>

Theme:

<style name="App.Button">
  <item name="colorPrimary">@color/green</item>
  <item name="colorPrimaryVariant">@color/green</item>
  <item name="colorOnPrimary">@color/white</item>
  <item name="rippleColor">@color/white</item>
</style>
<style name="App.Button.Secondary">
  <item name="colorPrimary">@color/white_dirty</item>
  <item name="colorPrimaryVariant">@color/grey</item>
  <item name="colorOnPrimary">@color/grey</item>
  <item name="rippleColor">@color/grey_light_variant</item>
</style>

Layout:

<com.google.android.material.button.MaterialButton
   style="@style/App.WidgetStyle.Button"
   android:theme="@style/App.Button"
   .../>
<com.google.android.material.button.MaterialButton
   style="@style/App.WidgetStyle.Button"
   android:theme="@style/App.Button.Secondary"
   .../>

:)