one-column.css

/**
 * @file
 * CSS for the one column layout.
 */
.layout--one-column .l-header,
.layout--one-column .l-top,
.layout--one-column .l-messages,
.layout--one-column .l-container,
.layout--one-column .l-footer {
  width: 100%;
  margin-left: auto;
  margin-right: auto;
  -moz-box-sizing: border-box;
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
  clear: both;
}