css 宽度 百分比与数值加减

margin-left: calc(50% - 53px);margin-left:-webkit-calc(50% - 53px);margin-left:-moz-calc(50% - 53px);

width:calc(64%-15px);width:-webkit-calc(64% - 15px);width:-moz-calc(64% - 15px);margin-right: 15px;