two-column.css

/**
 * @file
 * CSS for the two column layout.
 */

/* Clearfix for all regions. */
.layout--two-column .l-header:after,
.layout--two-column .l-main-wrapper:after,
.layout--two-column .l-footer:after,
.layout--two-column .l-container:after,
.layout--two-column .l-content:after,
.layout--two-column .l-sidebar:after {
  content: "";
  display: table;
  clear: both;
}

.layout--two-column .l-header,
.layout--two-column .l-top,
.layout--two-column .l-messages,
.layout--two-column .l-container,
.layout--two-column .l-footer {
  width: 100%;
  margin-left: auto;
  margin-right: auto;
  box-sizing: border-box;
  clear: both;
}
.layout--two-column .l-content,
.layout--two-column .l-sidebar {
  padding: 0 15px;
  box-sizing: border-box;
}

@media all and (min-width: 851px) {
  .layout--two-column .l-content,
  .layout--two-column .l-sidebar {
    display: inline;
    float: left; /* LTR */
    position: relative;
  }
  [dir="rtl"] .layout--two-column .l-content,
  [dir="rtl"] .layout--two-column .l-sidebar {
    float: right;
  }
  .layout--two-column .l-content {
    margin-right: 30%;
    width: 70%;
  }
  [dir="rtl"] .layout--two-column .l-content {
    margin-left: 30%;
    margin-right: 0;
  }
  .layout--two-column .l-sidebar {
    width: 30%;
    margin-left: -30%; /* LTR */
  }
  [dir="rtl"] .layout--two-column .l-sidebar {
    margin-right: -30%;
  }
}