Support transparent color

app/assets/sample_data.json

@@ -40,7 +40,8 @@
    },
    {
       "attributes":{
-         "italic":true
+         "italic":true,
+         "background":"transparent"
       },
       "insert":"library"
    },

app/lib/pages/home_page.dart

@@ -79,7 +79,7 @@ class _HomePageState extends State<HomePage> {
               scrollController: ScrollController(),
               scrollable: true,
               focusNode: _focusNode,
-              autoFocus: true,
+              autoFocus: false,
               readOnly: false,
               enableInteractiveSelection: true,
               expands: false,

lib/widgets/text_line.dart

@@ -115,6 +115,9 @@ class TextLine extends StatelessWidget {
       return Color.fromRGBO(int.parse(arr[0]), int.parse(arr[1]),
           int.parse(arr[2]), double.parse(arr[3]));
     }
+    if (s == 'transparent') {
+      return Colors.transparent;
+    }
     String hex = s.replaceFirst('#', '');
     hex = hex.length == 6 ? 'ff' + hex : hex;
     int val = int.parse(hex, radix: 16);