css: Improve padding of node title and ports

src/style.css

@@ -39,9 +39,12 @@ graphview {
     background-color: @view_bg_color;
 }
 
-port {
-    padding-top: 3px;
-    padding-bottom: 3px;
+node label.heading {
+	padding: 4px;
+}
+
+port label {
+    padding: 3px;
 }
 
 port-handle {

src/ui/graph/node.rs

@@ -60,6 +60,8 @@ mod imp {
             klass.set_layout_manager_type::<gtk::BoxLayout>();
 
             klass.bind_template();
+
+            klass.set_css_name("node");
         }
 
         fn instance_init(obj: &glib::subclass::InitializingObject<Self>) {

src/ui/graph/node.ui

@@ -34,4 +34,3 @@
     </child>
   </template>
 </interface>
-