fix grid area, fixes #85

Author: jogibear9988

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

@@ -527,6 +527,17 @@ public void CssGridAreaSingleValueLegal()
             Assert.AreEqual("2 / auto / auto / auto", property.Value);
         }
 
+        [Test]
+        public void CssGridAreaSingleTextValueLegal()
+        {
+            var source = "#nav-header {grid-area: navheader; }";
+            var css = ParseStyleSheet(source);
+            var text = css.Rules[0].CssText;
+
+            var expected = "#nav-header { grid-area: navheader / navheader / navheader / navheader }";
+            Assert.AreEqual(expected, text);
+        }
+
         [Test]
         public void CssGridAutoFlowAndRepeatLegal()
         {

src/AngleSharp.Css/Declarations/GridAreaDeclaration.cs

@@ -74,6 +74,11 @@ private static ICssValue GetItemSimple(CssTupleValue tuple, Int32 index)
                     }
                 }
 
+                if (tuple.Items.Length > 0 && !int.TryParse(tuple.Items[0].CssText, out int _))
+                {
+                    return tuple.Items[0];
+                }
+
                 return new Constant<Object>(CssKeywords.Auto, null);
             }
         }