Fixed theming bug in button and button group.

lib/pixi/buttongroup.html

@@ -101,6 +101,7 @@ const buttonGroup5 = new ButtonGroup({
         {label: 'ButtonGroup'},
         {label: 'of', active: true},
         {label: 'type'},
+        {minWidth: 30, style: 'link'},
         {label: 'checkbox', active: true}
     ],
     margin: 6,
@@ -272,6 +273,8 @@ const buttons16 = []
 for (let i = 1; i < 101; i++) {
     buttons16.push({label: `Button ${i}`, stroke: Math.floor(Math.random() * 16777215), strokeWidth: 3, radius: 16})
 }
+
+buttons16.splice(6, 0, {minWidth: 50, style: 'link'})
 const buttonGroup16 = new ButtonGroup({
     x: 90,
     y: 1040,