/* 3カラム+マージン(隙間)の合計幅 */

body>div.uk-container.uk-container-center{

width: 1000px; 

}

/* 左カラムの幅 */

body>div.uk-container.uk-container-center>div.uk-grid>div[class*=uk-width-].sidebar.left_side {

width: 240px;

}

/* メインカラムの幅 */

body>div.uk-container.uk-container-center>div.uk-grid>div[class*=uk-width-].sidebar.left_side+.main_content {

width: 440px;

}

/* 右カラムの幅 */

body>div.uk-container.uk-container-center>div.uk-grid>div[class*=uk-width-].sidebar.right_side {

width: 300px;

}