用此mixins可按设定宽度固定表格的宽度，具体布局原理详见表格布局原理

_table-width.scss

/**
 * Fix table width
 *
 * Usage:
 * ```scss
 * .table {
 *   @include table-width(60px 120px 60px initial 30em 50rem);
 * }
 * ```
 */
@mixin table-width($table-cell-width) {
  @for $i from 1 through length($table-cell-width) {
    th:nth-child(#{length($table-cell-width)}n+#{$i}) {
      width: nth($table-cell-width, $i);
    }
  }
}