silverstripe-framework/scss/SelectionGroup.scss

.SelectionGroup {
	padding: 0px;
	clear : both;

	li {
		list-style-type: none;
		float : left;
		width: 100%;
		clear : both;
	}
	li input.selector {
		width: 20px;
		float : left;
	}
	li > div.field {
		display: none;
		font-size: 1em;
	}
	li input, .right .SelectionGroup li label {
		display: block;
	}	
	li.selected > div.field {
		margin-left: 30px;
		display: block;
		margin-bottom: 1em;
	}	
	li.selected label.selector {
		font-weight: bold;
	}
}

.mainblock.allassets ul {
   padding: 0 0 0 10px;
   height:100px;
   overflow-y:scroll;
}	
.mainblock.allassets ul li {
   width: 150px;
}