@adobe/spectrum-css/dist/components/miller/index-vars.css

The Spectrum CSS top-level backwards compatible package

.spectrum-MillerColumns {
  overflow-x: auto;
  white-space: nowrap;
  -webkit-user-select: none;
     -moz-user-select: none;
      -ms-user-select: none;
          user-select: none;
  padding: 8px 0;
}

.spectrum-MillerColumns-item {
  display: inline-block;
  width: var(--spectrum-miller-column-width, var(--spectrum-global-dimension-static-size-3400));
  vertical-align: top;
  outline: none;
  margin: 0;
  padding: 0;
  margin-right: 8px;
  overflow: auto;
  height: 100%;
}

.spectrum-MillerColumns-item:first-child {
    margin-left: 8px;
  }