Started with cleanup

src/AngleSharp.Css/Declarations/BorderBottomDeclaration.cs

@@ -4,6 +4,7 @@ namespace AngleSharp.Css.Declarations
     using AngleSharp.Css.Values;
     using AngleSharp.Text;
     using System;
+    using System.Linq;
     using static ValueConverters;
 
     static class BorderBottomDeclaration
@@ -28,20 +29,13 @@ namespace AngleSharp.Css.Declarations
 
         sealed class BorderBottomAggregator : IValueAggregator, IValueConverter
         {
-            public ICssValue Convert(StringSource source)
-            {
-                return BorderSideConverter.Convert(source);
-            }
+            public ICssValue Convert(StringSource source) => BorderSideConverter.Convert(source);
 
             public ICssValue Merge(ICssValue[] values)
             {
-                var width = values[0];
-                var style = values[1];
-                var color = values[2];
-
-                if (width != null || style != null || color != null)
+                if (values.Length == 3)
                 {
-                    return new CssTupleValue(new[] { width, style, color });
+                    return new CssTupleValue(values);
                 }
 
                 return null;
@@ -49,16 +43,9 @@ namespace AngleSharp.Css.Declarations
 
             public ICssValue[] Split(ICssValue value)
             {
-                var options = value as CssTupleValue;
-
-                if (options != null)
+                if (value is CssTupleValue options)
                 {
-                    return new[]
-                    {
-                        options.Items[0],
-                        options.Items[1],
-                        options.Items[2],
-                    };
+                    return options.ToArray();
                 }
 
                 return null;

src/AngleSharp.Css/Declarations/BorderColorDeclaration.cs

@@ -5,6 +5,7 @@ namespace AngleSharp.Css.Declarations
     using AngleSharp.Css.Values;
     using AngleSharp.Text;
     using System;
+    using System.Linq;
     using static ValueConverters;
 
     static class BorderColorDeclaration
@@ -32,21 +33,13 @@ namespace AngleSharp.Css.Declarations
         {
             private static readonly IValueConverter converter = Or(CurrentColorConverter.Periodic(), AssignInitial());
 
-            public ICssValue Convert(StringSource source)
-            {
-                return converter.Convert(source);
-            }
+            public ICssValue Convert(StringSource source) => converter.Convert(source);
 
             public ICssValue Merge(ICssValue[] values)
             {
-                var top = values[0];
-                var right = values[1];
-                var bottom = values[2];
-                var left = values[3];
-
-                if (top != null && right != null && bottom != null && left != null)
+                if (values.Length > 0)
                 {
-                    return new CssPeriodicValue(new[] { top, right, bottom, left });
+                    return new CssPeriodicValue(values);
                 }
 
                 return null;
@@ -54,17 +47,9 @@ namespace AngleSharp.Css.Declarations
 
             public ICssValue[] Split(ICssValue value)
             {
-                var periodic = value as CssPeriodicValue;
-
-                if (periodic != null)
+                if (value is CssPeriodicValue periodic)
                 {
-                    return new[]
-                    {
-                        periodic.Top,
-                        periodic.Right,
-                        periodic.Bottom,
-                        periodic.Left,
-                    };
+                    return periodic.ToArray();
                 }
 
                 return null;

src/AngleSharp.Css/Values/Multiples/CssPeriodicValue.cs

@@ -4,7 +4,6 @@ namespace AngleSharp.Css.Values
     using System;
     using System.Collections;
     using System.Collections.Generic;
-    using System.Linq;
 
     /// <summary>
     /// Represents a periodic CSS value.
@@ -108,10 +107,15 @@ namespace AngleSharp.Css.Values
 
         #region Methods
 
-        IEnumerator<ICssValue> IEnumerable<ICssValue>.GetEnumerator() =>
-            _values.OfType<ICssValue>().GetEnumerator();
+        IEnumerator<ICssValue> IEnumerable<ICssValue>.GetEnumerator()
+        {
+            yield return Top;
+            yield return Right;
+            yield return Bottom;
+            yield return Left;
+        }
 
-        IEnumerator IEnumerable.GetEnumerator() => _values.GetEnumerator();
+        IEnumerator IEnumerable.GetEnumerator() => ((IEnumerable<ICssValue>)this).GetEnumerator();
 
         #endregion
     }