Update elfinder.full.css

Fix button size: box-sizing: content-box;
bootstrap.css conflict: box-sizing: border-box;
<pre>
.elfinder .elfinder-button {
	width:16px;
	height:16px;
	margin:0;
	padding:4px;
	float:left;
	overflow:hidden;
	position:relative;
	border:0 solid;
        -webkit-box-sizing: content-box;
	-moz-webkit-box-sizing: content-box;
	-ms-webkit-box-sizing: content-box;
	-o-webkit-box-sizing: content-box;
}
</pre>