ant-design-vue/components/vc-table/assets/bordered.less

@tablePrefixCls: rc-table;
@table-border-color: #e9e9e9;

.@{tablePrefixCls}.bordered {
  table {
    border-collapse: collapse;
  }
  th, td {
    border: 1px solid @table-border-color;
  }
}