自適應計算n欄的寬度

網頁想要排版成n欄一排

<div class="grid">
  <div class="grid__item"></div>
</div>

.grid {
  display: flex;
  flex-wrap: wrap;
    &__item {
      margin-bottom: $gutter;
      width: calc((100% - 2 * #{$gutter}) / 3);
      &:not(:nth-child(3n)) {
        margin-right: $gutter;
      }
  }
}