Add style for leading

lib/widgets/default_styles.dart

@@ -59,6 +59,7 @@ class DefaultStyles {
   final DefaultTextBlockStyle? code;
   final DefaultTextBlockStyle? indent;
   final DefaultTextBlockStyle? align;
+  final DefaultTextBlockStyle? leading;
 
   DefaultStyles(
       {this.h1,
@@ -77,6 +78,7 @@ class DefaultStyles {
       this.code,
       this.indent,
       this.align,
+      this.leading,
       this.sizeSmall,
       this.sizeLarge,
       this.sizeHuge});
@@ -183,6 +185,8 @@ class DefaultStyles {
             baseStyle, baseSpacing, const Tuple2(0.0, 6.0), null),
         align: DefaultTextBlockStyle(
             baseStyle, const Tuple2(0.0, 0.0), const Tuple2(0.0, 0.0), null),
+        leading: DefaultTextBlockStyle(
+            baseStyle, const Tuple2(0.0, 0.0), const Tuple2(0.0, 0.0), null),
         sizeSmall: const TextStyle(fontSize: 10.0),
         sizeLarge: const TextStyle(fontSize: 18.0),
         sizeHuge: const TextStyle(fontSize: 22.0));
@@ -206,6 +210,7 @@ class DefaultStyles {
         code: other.code ?? code,
         indent: other.indent ?? indent,
         align: other.align ?? align,
+        leading: other.leading ?? leading,
         sizeSmall: other.sizeSmall ?? sizeSmall,
         sizeLarge: other.sizeLarge ?? sizeLarge,
         sizeHuge: other.sizeHuge ?? sizeHuge);

lib/widgets/text_block.dart

@@ -141,7 +141,7 @@ class EditableTextBlock extends StatelessWidget {
         index: index,
         indentLevelCounts: indentLevelCounts,
         count: count,
-        style: defaultStyles!.paragraph!.style,
+        style: defaultStyles!.leading!.style,
         attrs: attrs,
         width: 32.0,
         padding: 8.0,
@@ -150,20 +150,20 @@ class EditableTextBlock extends StatelessWidget {
 
     if (attrs[Attribute.list.key] == Attribute.ul) {
       return _BulletPoint(
-        style: defaultStyles!.paragraph!.style
-            .copyWith(fontWeight: FontWeight.bold),
+        style:
+            defaultStyles!.leading!.style.copyWith(fontWeight: FontWeight.bold),
         width: 32,
       );
     }
 
     if (attrs[Attribute.list.key] == Attribute.checked) {
       return _Checkbox(
-          style: defaultStyles!.paragraph!.style, width: 32, isChecked: true);
+          style: defaultStyles!.leading!.style, width: 32, isChecked: true);
     }
 
     if (attrs[Attribute.list.key] == Attribute.unchecked) {
       return _Checkbox(
-          style: defaultStyles!.paragraph!.style, width: 32, isChecked: false);
+          style: defaultStyles!.leading!.style, width: 32, isChecked: false);
     }
 
     if (attrs.containsKey(Attribute.codeBlock.key)) {