silverstripe-cms/css/editor.css

/**
 * Default Editor Styles for the CMS
 */

.typography .mceItemFlash {
	border: 1px dotted #f00;
}

body.mceContentBody {
	min-height: 200px;
	font-size: 62.5%;
}

/*
body.mceContentBody a.broken {
	background-color: #FF7B71;
	border: 1px red solid;
	color: #fff; 
 	padding: 1px; 
 	text-decoration: underline;
}
*/