Simplify theming for Button widget

core/src/background.rs

@@ -11,6 +11,19 @@ pub enum Background {
     // TODO: Add image variant
 }
 
+impl Background {
+    /// Increases the translucency of the [`Background`]
+    /// by the given factor.
+    pub fn transparentize(self, factor: f32) -> Self {
+        match self {
+            Self::Color(color) => Self::Color(color.transparentize(factor)),
+            Self::Gradient(gradient) => {
+                Self::Gradient(gradient.transparentize(factor))
+            }
+        }
+    }
+}
+
 impl From<Color> for Background {
     fn from(color: Color) -> Self {
         Background::Color(color)

core/src/color.rs

@@ -151,6 +151,14 @@ impl Color {
     pub fn inverse(self) -> Color {
         Color::new(1.0f32 - self.r, 1.0f32 - self.g, 1.0f32 - self.b, self.a)
     }
+
+    /// Transparentizes the [`Color`] by the given factor.
+    pub fn transparentize(self, factor: f32) -> Color {
+        Self {
+            a: self.a * factor,
+            ..self
+        }
+    }
 }
 
 impl From<[f32; 3]> for Color {

core/src/gradient.rs

@@ -13,11 +13,11 @@ pub enum Gradient {
 
 impl Gradient {
     /// Adjust the opacity of the gradient by a multiplier applied to each color stop.
-    pub fn mul_alpha(mut self, alpha_multiplier: f32) -> Self {
+    pub fn transparentize(mut self, factor: f32) -> Self {
         match &mut self {
             Gradient::Linear(linear) => {
                 for stop in linear.stops.iter_mut().flatten() {
-                    stop.color.a *= alpha_multiplier;
+                    stop.color.a *= factor;
                 }
             }
         }