<section>
  <div></div>
  <div></div>
  <div></div>
</section>

section {
  border: 0.5em solid #efefef;
  display: flex;
  gap: 1em;
  margin: 1em;
  overflow: hidden;
  padding: 6px;
}
div {
  box-shadow: 0 0 6px 1px #f00;
  height: 300px;
  width: 300px;
}