--- a/layout/style/nsCSSValue.cpp
+++ b/layout/style/nsCSSValue.cpp
@@ -473,16 +473,23 @@ void nsCSSValue::SetFloatColorValue(floa
   Reset();
   mUnit = aUnit;
   MOZ_ASSERT(IsFloatColorUnit(), "bad unit");
   mValue.mFloatColor =
     new nsCSSValueFloatColor(aComponent1, aComponent2, aComponent3, aAlpha);
   mValue.mFloatColor->AddRef();
 }
 
+void
+nsCSSValue::SetRGBAColorValue(const RGBAColorData& aValue)
+{
+  SetFloatColorValue(aValue.mR, aValue.mG, aValue.mB,
+                     aValue.mA, eCSSUnit_PercentageRGBAColor);
+}
+
 void nsCSSValue::SetArrayValue(nsCSSValue::Array* aValue, nsCSSUnit aUnit)
 {
   Reset();
   mUnit = aUnit;
   MOZ_ASSERT(UnitHasArrayValue(), "bad unit");
   mValue.mArray = aValue;
   mValue.mArray->AddRef();
 }

--- a/layout/style/nsCSSValue.h
+++ b/layout/style/nsCSSValue.h
@@ -294,16 +294,62 @@ public:
     NS_INLINE_DECL_REFCOUNTING(FontFamilyListRefCnt);
 
 private:
     ~FontFamilyListRefCnt() {
         MOZ_COUNT_DTOR(FontFamilyListRefCnt);
     }
 };
 
+struct RGBAColorData
+{
+  // 1.0 means 100% for all components, but the value may fall outside
+  // the range of [0.0, 1.0], so it is necessary to clamp them when
+  // converting to nscolor.
+  float mR;
+  float mG;
+  float mB;
+  float mA;
+
+  RGBAColorData() = default;
+  MOZ_IMPLICIT RGBAColorData(nscolor aColor)
+    : mR(NS_GET_R(aColor) * (1.0f / 255.0f))
+    , mG(NS_GET_G(aColor) * (1.0f / 255.0f))
+    , mB(NS_GET_B(aColor) * (1.0f / 255.0f))
+    , mA(NS_GET_A(aColor) * (1.0f / 255.0f))
+  {}
+  RGBAColorData(float aR, float aG, float aB, float aA)
+    : mR(aR), mG(aG), mB(aB), mA(aA) {}
+
+  bool operator==(const RGBAColorData& aOther) const
+  {
+    return mR == aOther.mR && mG == aOther.mG &&
+           mB == aOther.mB && mA == aOther.mA;
+  }
+  bool operator!=(const RGBAColorData& aOther) const
+  {
+    return !(*this == aOther);
+  }
+
+  nscolor ToColor() const
+  {
+    return NS_RGBA(ClampColor(mR * 255.0f),
+                   ClampColor(mG * 255.0f),
+                   ClampColor(mB * 255.0f),
+                   ClampColor(mA * 255.0f));
+  }
+
+  RGBAColorData WithAlpha(float aAlpha) const
+  {
+    RGBAColorData result = *this;
+    result.mA = aAlpha;
+    return result;
+  }
+};
+
 } // namespace css
 } // namespace mozilla
 
 enum nsCSSUnit {
   eCSSUnit_Null         = 0,      // (n/a) null unit, value is not specified
   eCSSUnit_Auto         = 1,      // (n/a) value is algorithmic
   eCSSUnit_Inherit      = 2,      // (n/a) value is inherited
   eCSSUnit_Initial      = 3,      // (n/a) value is default UA value
@@ -766,16 +812,17 @@ public:
   void SetFloatValue(float aValue, nsCSSUnit aUnit);
   void SetStringValue(const nsString& aValue, nsCSSUnit aUnit);
   void SetColorValue(nscolor aValue);
   void SetIntegerColorValue(nscolor aValue, nsCSSUnit aUnit);
   void SetFloatColorValue(float aComponent1,
                           float aComponent2,
                           float aComponent3,
                           float aAlpha, nsCSSUnit aUnit);
+  void SetRGBAColorValue(const mozilla::css::RGBAColorData& aValue);
   void SetArrayValue(nsCSSValue::Array* aArray, nsCSSUnit aUnit);
   void SetURLValue(mozilla::css::URLValue* aURI);
   void SetImageValue(mozilla::css::ImageValue* aImage);
   void SetGradientValue(nsCSSValueGradient* aGradient);
   void SetTokenStreamValue(nsCSSValueTokenStream* aTokenStream);
   void SetGridTemplateAreas(mozilla::css::GridTemplateAreasValue* aValue);
   void SetFontFamilyListValue(mozilla::css::FontFamilyListRefCnt* aFontListValue);
   void SetPairValue(const nsCSSValuePair* aPair);