Added widget-label style def && fab css

IPython/html/static/notebook/less/widgetarea.less

@@ -1,19 +1,23
+.widget-label {
+    min-width: 300px;
+}
+
 div.widget-container {
     .box-flex2();
     .border-box-sizing();
 }
 
 div.widget-area {
     page-break-inside: avoid;
     .hbox();
 }
 
 /* This class is for the widget subarea inside the widget_area and after
    the prompt div. */
 div.widget-subarea {
     padding: 0.44em 0.4em 0.4em 1px;
     margin-left: 6px;
     .border-box-sizing();
     .vbox();
     .box-flex2()
 }