Challenge 1: A Reusable Button Style — Solution

// res/values/colors.xml
<resources>
    <color name="secondary_bg">#2BB673</color>
    <color name="secondary_text">#FFFFFF</color>
</resources>

// res/values/styles.xml
<resources>
    <style name="SecondaryButton">
        <item name="android:backgroundTint">@color/secondary_bg</item>
        <item name="android:textColor">@color/secondary_text</item>
    </style>
</resources>

// activity_main.xml
<Button
    style="@style/SecondaryButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Save" />

<Button
    style="@style/SecondaryButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Cancel" />

Notes:
- Both Buttons reference the same style="@style/SecondaryButton" — any
  future change to SecondaryButton (a new color, added padding, etc.)
  updates both Buttons at once, without editing either <Button> tag.
- The style references color RESOURCES (@color/secondary_bg,
  @color/secondary_text) rather than hardcoded hex values — this is what
  keeps the style dark-mode-compatible if secondary_bg/secondary_text
  are later given values-night overrides (Challenge 3).
- A style bundles multiple attributes (backgroundTint AND textColor
  here) into one reusable named unit — the direct equivalent of a CSS
  class bundling several property declarations under one class name.