Improve the appearance of <sky-checkbox>

sky/framework/sky-box/sky-box.sky

Index: sky/framework/sky-box/sky-box.sky
diff --git a/sky/framework/sky-box/sky-box.sky b/sky/framework/sky-box/sky-box.sky
index ed21ebd01ee6f4fc7a2ee6b5d5d4efd62a638a48..3bee0176b252544922d0e446d3792b3ab930fe08 100644
--- a/sky/framework/sky-box/sky-box.sky
+++ b/sky/framework/sky-box/sky-box.sky
@@ -15,16 +15,20 @@
       border: 1px solid gray;
       margin: 10px;
     }
-    #title {
+    .title {
       text-align: center;
       font-size: 10px;
+      padding: 8px 8px 4px 8px;
+    }
+    .content {
+      padding: 4px 8px 8px 8px;
     }
     div {
-      flex: 1 100%;
+      flex: 1;
     }
   </style>
-  <div id='title'>{{ title }}</div>
-  <div><content></content></div>
+  <div class="title">{{ title }}</div>
+  <div class="content"><content></content></div>
 </template>
 <script>
 module.exports = class extends SkyElement {