struct Style : ChStyle<Style> {
    Value look[4];
    Color monocolor[4], textcolor[4];
    Point pressoffset;
    int   focusmargin;
    int   overpaint;
    Font  font;
    Image ok, cancel, exit;
    bool  transparent;
    bool  focus_use_ok;

    // Animation properties
  enum AnimationFinishBehavior {
        GOTO_FIRST,      // Go to the first frame when the animation is interrupted
        GOTO_LAST,       // Go to the last frame when the animation is interrupted
        COMPLETE,        // Complete the animation normally when interrupted
        COMPLETE_FAST,   // Complete the animation quickly when interrupted
        HOLD,            // Hold the current frame when the animation is interrupted
        REVERSE          // Reverse the animation when interrupted
    };

    AnimationFinishBehavior animationFinishBehavior;
    double animation_duration; // Duration of the animation in seconds
    double (*animation_easing_function)(double); // Easing function for the animation
};

template <class T>
struct ChStyle {
    // ...
    std::vector<T> animationStates;
    double animationDuration;
    EasingFunction easingFunction;
    // ...
};

void Button::OnMouseEnter() {
    // notify Update the animation state
    // ...

    // notify Start the animation
    // ...
}

void Button::OnMouseLeave() {
    // notify Update the animation state
    // ...

    // notify Start the animation
    // ...
}