/* @import url('http://example.com/example_style.css'); */

/***********************************************/
/* CSS @imports must be at the top of the file */
/* Add them above this section                 */
/***********************************************/

/*****************************************/
/* Start your style declarations here    */
/*****************************************/

<style>
/* Desktop only (≥1024 px) */
@media (min-width: 1024px) {
  /* 1) wipe any existing side-margins */
  body > * {
    margin-left: 0 !important;
    margin-right: 0 !important;
  }

  /* 2) add the 200 px gutter to everything except header + footer */
  body > *:not(header):not(footer) {
    margin-left: 200px !important;
    margin-right: 200px !important;
  }
}
</style>