JSFiddle - React, Tailwind, and code Playground

HTML

<div id="ext-comp-1063" class=" x-window x-window-plain x-resizable-pinned">
   <div class="x-window-tl">
      <div class="x-window-tr">
         <div class="x-window-tc">
            <div class="x-window-header x-unselectable x-panel-icon x-deluge-remove-window-icon x-window-draggable" id="ext-gen215">
               <div class="x-tool x-tool-close" id="ext-gen221">&nbsp;</div>
               <span class="x-window-header-text" id="ext-gen226" data-content="this one">This one</span>
            </div>
         </div>
      </div>
   </div>
   <div class="x-window-bl" id="ext-gen219">
      <div class="x-window-br">
         <div class="x-window-bc">
            <div class="x-window-footer x-panel-btns" id="ext-gen218" style="width: 328px;">
               <div id="ext-comp-1064" class="x-panel-fbar x-small-editor x-toolbar-layout-ct" style="width: auto;">
                  <table cellspacing="0" class="x-toolbar-ct">
                     <tbody>
                        <tr>
                           <td class="x-toolbar-right" align="right">
                              <table cellspacing="0" class="x-toolbar-right-ct">
                                 <tbody>
                                    <tr>
                                       <td>
                                          <table cellspacing="0">
                                             <tbody>
                                                <tr class="x-toolbar-right-row">
                                                   <td class="x-toolbar-cell" id="ext-gen227">
                                                      <table id="ext-comp-1065" cellspacing="0" class="x-btn x-btn-noicon" style="width: auto;">
                                                         <tbody class="x-btn-small x-btn-icon-small-left">
                                                            <tr>
                                                               <td class="x-btn-ml"><i>&nbsp;</i></td>
               ...

CSS

.x-window > .x-window-bl > .x-window-br > .x-window-bc > .x-window-footer > .x-panel-fbar > .x-toolbar-ct > tbody > tr > td > table > tbody > tr > td > table > tbody > .x-toolbar-right-row > .x-toolbar-cell > table > .x-btn-small > tr > td:nth-child(2) > em > button{
  background-color:red
}

[data-content="this one"] {
    color: red;
}