Fixed edge case for none in grid-template

Author: FlorianRappl

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

@@ -768,5 +768,13 @@ public void CssRuleWithOnlyGridTemplateAreasLegal_Issue27()
             var text = rule.CssText;
             Assert.AreEqual(snippet, text);
         }
+
+        [Test]
+        public void CssGridTemplateLonghands_Issue68()
+        {
+            var snippet = "grid-template-areas: none; grid-template-columns: none; grid-template-rows: none";
+            var style = ParseDeclarations(snippet);
+            Assert.AreEqual("grid-template: none", style.CssText);
+        }
     }
 }

src/AngleSharp.Css/Values/Composites/CssGridTemplateValue.cs

@@ -61,7 +61,11 @@ public String CssText
                 var rows = String.Empty;
                 var cols = _columns?.CssText;
 
-                if (_areas != null)
+                if (_areas is Constant<object> || _columns is Constant<object> || _rows is Constant<object>)
+                {
+                    return CssKeywords.None;
+                }
+                else if (_areas != null)
                 {
                     var areas = ((CssTupleValue)_areas).Items;
                     var rowItems = ((CssTupleValue)_rows).Items;
@@ -89,7 +93,7 @@ public String CssText
 
                 if (!String.IsNullOrEmpty(cols))
                 {
-                    return String.Concat(rows, " / ",cols);
+                    return String.Concat(rows, " / ", cols);
                 }
 
                 return rows;