JSFiddle - React, Tailwind, and code Playground

HTML

<html>
	<head>
		<meta charset="utf-8">
		<title>CKEditor</title>
		<script src="https://cdn.ckeditor.com/ckeditor5/11.2.0/classic/ckeditor.js"></script>
	</head>
	<body>
		<textarea name="content" id="editor">This is some sample content.</textarea>
	</body>
</html>

CSS

.ck.ck-editor__main>.ck-editor__editable:not(.ck-focused) {
  border:none
}
.ck-rounded-corners .ck.ck-editor__top .ck-sticky-panel .ck-toolbar, .ck.ck-editor__top .ck-sticky-panel .ck-toolbar.ck-rounded-corners {
  border:none;
  background: transparent;
}

JavaScript

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        toolbar: ['bold'],
    } )
    .catch( error => {
        console.log( error );
    } );