flex 子の伸び縮みをまとめて書く

<div class="row">
  <span>固定</span>
  <span class="grow">ここが伸びる</span>
  <span>固定</span>
</div>

.row {
  display: flex;
  gap: 0.4rem;
}
.row > .grow {
  flex: 1;
  background: #efeef8;
  padding: 0.4rem 0.65rem;
}
.row > span {
  background: #efeef8;
  padding: 0.4rem 0.65rem;
}