如何样式化CKEditors的单个实例？

<script src="path/to/ckeditor.js"></script>

<textarea id="editor"></textarea>

CKEDITOR.replace('editor');

#cke_editor {
  background-color: #f2f2f2;
}

CKEDITOR.replace('editor', {
  toolbar: [
    { name: 'document', items: ['Source', '-', 'Save'] },
    { name: 'clipboard', items: ['Cut', 'Copy', 'Paste', 'PasteText', 'PasteFromWord', '-', 'Undo', 'Redo'] },
    { name: 'styles', items: ['Format', 'Font', 'FontSize'] },
    { name: 'basicstyles', items: ['Bold', 'Italic', 'Underline', 'Strike', 'Subscript', 'Superscript', '-', 'RemoveFormat'] },
    { name: 'paragraph', items: ['NumberedList', 'BulletedList', '-', 'Outdent', 'Indent', '-', 'Blockquote'] },
    { name: 'links', items: ['Link', 'Unlink'] },
    { name: 'insert', items: ['Image', 'Table', 'HorizontalRule', 'SpecialChar'] },
    { name: 'tools', items: ['Maximize'] },
    { name: 'editing', items: ['Scayt'] }
  ]
});