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

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

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

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

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

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

<div class="alert">
  <p>您的浏览器暂时还不支持CSS的<code>:has</code>选择器。请使用 Safari 15.4 或 Chrome Canary 最新版本查看(^_^)!</p>
</div>

@import url("https://fonts.googleapis.com/css2?family=Exo:wght@600&display=swap");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  width: 100vw;
  min-height: 100vh;
  font-family: "Exo", Arial, sans-serif;
  background-color: #557;
  display: flex;
  justify-content: center;
  align-items: flex-start;
  align-content: flex-start;
  flex-wrap: wrap;
  gap: 20px;
  padding: 80px 20px 20px;
}

section {
  width: 40vw;
  padding: 10px;
  border: 1px dashed #00ff16;
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  align-items: flex-start;
  gap: 10px;
  margin: 10px auto;
  border-radius: 6px;
}

section > div {
  flex: 1 1 calc((100% - 10px * 2) / 3);
  aspect-ratio: 16 / 9;
  border-radius: 10px;
  background-color: #ffa200;
}

section:has(div:nth-child(3n + 1):last-child)::after {
  content: "";
  display: flex;
  flex: 1 1 calc(((100% - 10px * 2) / 3) * 2 + 10px);
  min-height: 1px;
  background-color: #09fcae;
}

section:has(div:nth-child(3n + 2):last-child)::after {
  content: "";
  display: flex;
  flex: 1 1 calc((100% - 10px * 2) / 3);
  min-height: 1px;
  background-color: #09fcae;
}

.alert {
  display: flex;
  justify-content: center;
  position: fixed;
  padding: 1rem;
  background-color: #ffeeee;
  font-size: 0.75rem;
  top: 0;
  left: 0;
  right: 0;
  color: red;
}

.alert code {
  display: inline-flex;
  padding: 0.25em 0.5em;
  font-weight: bold;
  background-color: #3f51b5;
  color: #fff;
  border-radius: 3px;
  margin: 0 5px;
}

@supports selector(:has(*)) {
  .alert {
    display: none;
  }
}