Fix csstext not outputting the liniar angle that was parsed

Author: Frank

src/AngleSharp.Css.Tests/Declarations/CssBackgroundProperty.cs

@@ -661,5 +661,16 @@ public void CssBackgroundImageDataUrlLegal()
             Assert.IsTrue(property.HasValue);
             Assert.AreEqual("url(\"" + url + "\")", property.Value);
         }
+
+        [Test]
+        public void CssBackgroundImageLinearGradientLegal()
+        {
+            var source = "background-image: linear-gradient(to right, rgba(255, 0, 0, 1), rgba(0, 0, 255, 1))";
+            var property = ParseDeclaration(source);
+            Assert.IsTrue(property.HasValue);
+
+            var expected = "linear-gradient(90deg, rgba(255, 0, 0, 1), rgba(0, 0, 255, 1))";
+            Assert.AreEqual(expected, property.Value);
+        }
     }
 }

src/AngleSharp.Css.Tests/Declarations/CssBorderImageProperty.cs

@@ -1,4 +1,4 @@
-namespace AngleSharp.Css.Tests.Declarations
+namespace AngleSharp.Css.Tests.Declarations
 {
     using NUnit.Framework;
     using static CssConstructionFunctions;
@@ -39,7 +39,7 @@ public void CssBorderImageSourceLinearGradientLegal()
             Assert.IsFalse(property.IsImportant);
             Assert.IsFalse(property.IsInherited);
             Assert.IsTrue(property.HasValue);
-            Assert.AreEqual("linear-gradient(rgba(255, 0, 0, 1), rgba(255, 255, 0, 1))", property.Value);
+            Assert.AreEqual("linear-gradient(0deg, rgba(255, 0, 0, 1), rgba(255, 255, 0, 1))", property.Value);
         }
 
         [Test]

src/AngleSharp.Css.Tests/Values/Gradient.cs

@@ -29,7 +29,9 @@ public void InRadialGradient()
         [Test]
         public void BackgroundImageLinearGradientWithAngle()
         {
-            var source = "background-image: linear-gradient(135deg, red, blue)";
+            var red = Color.Red;
+            var blue = Color.Blue;
+            var source = $"background-image: linear-gradient(135deg, {red.CssText}, {blue.CssText})";
             var property = ParseDeclaration(source);
             Assert.IsTrue(property.HasValue);
             Assert.IsFalse(property.IsInitial);
@@ -41,8 +43,10 @@ public void BackgroundImageLinearGradientWithAngle()
             Assert.IsFalse(gradient.IsRepeating);
             Assert.AreEqual(Angle.TripleHalfQuarter, gradient.Angle);
             Assert.AreEqual(2, gradient.Stops.Length);
-            Assert.AreEqual(Color.Red, gradient.Stops.First().Color);
-            Assert.AreEqual(Color.Blue, gradient.Stops.Last().Color);
+            Assert.AreEqual(red, gradient.Stops.First().Color);
+            Assert.AreEqual(blue, gradient.Stops.Last().Color);
+
+            Assert.AreEqual(source, property.CssText);
         }
 
         [Test]

src/AngleSharp.Css/Values/Functions/CssLinearGradientValue.cs

@@ -69,7 +69,7 @@ public String CssText
             get
             {
                 var defaultAngle = _angle as Angle?;
-                var offset = defaultAngle.HasValue ? 0 : 1;
+                var offset = defaultAngle.HasValue ? 1 : 0;
                 var args = new String[_stops.Length + offset];
 
                 if (defaultAngle.HasValue)
@@ -80,7 +80,7 @@ public String CssText
                     {
                         if (angle.Value == value)
                         {
-                            args[0] = angle.Key;
+                            args[0] = angle.Value.CssText;
                             break;
                         }
                     }