WordPress/wp-includes/js/tinymce/themes/advanced/editor_content.css

body {
	padding: .5em;
	background: #fff;
	color: #000;
	font:  13px Verdana, Arial, Helvetica, sans-serif;
	line-height: 130%;
	scrollbar-3dlight-color: #F0F0EE;
	scrollbar-arrow-color: #676662;
	scrollbar-base-color: #F0F0EE;
	scrollbar-darkshadow-color: #DDDDDD;
	scrollbar-face-color: #E0E0DD;
	scrollbar-highlight-color: #F0F0EE;
	scrollbar-shadow-color: #F0F0EE;
	scrollbar-track-color: #F5F5F5;
}

.mceVisualAid {
	border: 1px dashed #bbb;
}