JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://yui.yahooapis.com/3.9.1/build/yui/yui-min.js"></script>
<script>
YUI.add('widget-buttons-patches', function(Y) {
    var WidgetStdMod = Y.WidgetStdMod,
        WidgetButtons = Y.WidgetButtons;
    
    Y.WidgetButtons.prototype._getButtonContainer = function(section, create){
        var sectionClassName = WidgetStdMod.SECTION_CLASS_NAMES[section],
            buttonsClassName = WidgetButtons.CLASS_NAMES.buttons,
            contentBox       = this.get('contentBox'),
            containerSelector, container;

        // Search for an existing buttons container within the section.
        containerSelector = '.' + sectionClassName + ' .' + buttonsClassName;

        // Search only inside the current widget
        contentBox.all(containerSelector).some(function(node){
            var widget = Y.Widget.getByNode(node),
                isBelongs = !widget || widget === this;
    
            if (isBelongs) {
                container = node;
            }
            return isBelongs;
        }, this);
    
        // Create the `container` if it doesn't already exist.
        if (!container && create) {
            container = Y.Node.create(this.BUTTONS_TEMPLATE);
            container.addClass(buttonsClassName);
        }

        return container;
    };
});

YUI.add('widget-stdmod-patches', function(Y) {
    var HEADER_CONTENT = 'headerContent',
        BODY_CONTENT = 'bodyContent',
        FOOTER_CONTENT = 'footerContent',
        FILL_HEIGHT = 'fillHeight',
        STD_HEADER = 'header',
        STD_BODY = 'body',
        STD_FOOTER = 'footer',
        StdMod = Y.WidgetStdMod,
        CONTENT_SUFFIX = 'Content',
        ContentUpdate = 'ContentUpdate',
        L = Y.Lang,
        UI = 'ui';
    
    Y.WidgetStdMod.prototype._syncUIStdMod = function(){
        var stdModParsed = this._stdModParsed;

        Y.each([STD_HEADER, STD_BODY, STD_FOOTER], function(section) {
            var content;

            if (!stdModParsed ||...

CSS

body {
    font-size: 12px;
    font-family: Tahoma, Geneva, sans-serif;
}

button.yui3-button {
    font-size: 12px;
}

.yui3-widget {
    margin : 4px;
    padding: 4px;
}

.yui3-child {
    background: yellow;
}

.yui3-main {
    background: green;
}

JavaScript

YUI({
    groups : {
        patches : {
            modules : {
              'widget-buttons-patches' : {
                  condition : {
                      name    : 'widget-buttons-patches',
                      trigger : 'widget-buttons',
                      test    : function(){
                          return true;
                      }
                  }
              },
              'widget-stdmod-patches' : {
                    condition : {
                        name    : 'widget-stdmod-patches',
                        trigger : 'widget-stdmod',
                        test    : function(){
                            return true;
                        }
                    }
                }
            }
        }
    }
}).use('widget-buttons', function(Y){
    var Main;
    
    Main = Y.Base.create('main', Y.Widget, [Y.WidgetStdMod], {
        renderUI : function() {
            var body = this.getStdModNode('body', true);
            
            console.log(body);
            
            //this.set('bodyContent', 'omg');
        }
    }/*, {
        ATTRS : {
            bodyContent : {
                value : 'initial'
            }
        }
    }*/);
    
    main = new Main({
        render : Y.one('body')
    });
    
    return;
  
});