@mixin flex($direction: row, $justify: flex-start, $align: stretch, $wrap: nowrap) {
  display: flex;
  flex-direction: $direction;
  justify-content: $justify;
  align-items: $align;
  flex-wrap: $wrap;
}

// 使用示例:
// @include flex(column, center, center);
// @include flex(row, space-between, center, wrap);