Making a div expand horizontally to fill its container

How do I rewrite the CSS code below so that "topRight" expands to fill the rest of "container" completely to its right edge? This is frustrating me because even if  Also in "container", how do I condense the 4 four border codes  into one?

Thanks!
John

body {
	background-color: #FFFFFF;
	/*background-image: url(../cowBoomBar2.jpg);*/
	background-repeat: repeat-x;
	margin-top: 0px;
}
#container {
	margin: 0 auto;
	width: 880px;
	height: 700px;
	background-repeat: no-repeat;
	font-family: "Gill Sans MT";
	font-size: 14px;
	position: relative;
	background-image: url(../CowBoom1_greenHeader.jpg);
	border-top-width: 1px;
	border-right-width: 1px;
	border-bottom-width: 1px;
	border-left-width: 1px;
	border-top-style: solid;
	border-right-style: solid;
	border-bottom-style: solid;
	border-left-style: solid;
	border-top-color: #000000;
	}
	
#mainBlock{
	height: 500px;
	color: #FF0000;
	font-family: "Gill Sans MT";
	background: #FFFFFF;
	margin-left: auto;
	padding: 0 0 0 10;
	width: 100%;
	float: left;
	margin-top: 138px;
	font-weight: bold;
        }
 
#topLeft {
	min-width: 200px;
	height: 380px;
	font-family: "Arial Black";
	font-size: 24px;
        margin-top: 30px
        margin-left: 0px;
	line-height: normal;
	width: 40%;
	color: #000000;
	font-weight: normal;
	float: left;
	padding-left: 40px;
	padding-top: 20px;
	margin-left: 0px;
	margin-top: 0px;
	border-bottom-width: medium;
	border-bottom-style: solid;
	border-bottom-color: #000000;
        }
#topRight{
	margin: 42 10 0;
	width: 40%;
	height: 400px;
	float: left;
	color: #000000;
	font-family: "Gill Sans MT";
	top: 0px;
	line-height: normal;
	font-size: 12px;
	padding-right: 30px;
	padding-left: 30px;
	text-align: justify;
	border-bottom-width: medium;
	border-bottom-style: solid;
	border-bottom-color: #000000;
	padding-top: 0px;
        }

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