content-visibility

概念定义

除非引擎能跳过，屏幕外内容的渲染成本与屏幕内相同。content-visibility: auto 声明元素在离屏时可跳过子树渲染但语义仍在，并在接近视口前恢复渲染，兼顾成本与语义完整性。

工作机制

该属性依赖包含：子树不影响外部布局，引擎才能推迟它。contain-intrinsic-size 提供子树高度的近似值，让可滚动区域保持稳定；交叉机制会在可见前留出边距恢复渲染，避免视口边缘弹入。

使用场景

长信息流、变更日志、规格式文档、管理后台表格。内征尺寸应按典型行高估算；浏览器会记住每元素上次渲染的高度，可在实测后修正。

常见误区

它不同于 display: none：跳过渲染仍保留页内查找、无障碍与锚点。缺 contain-intrinsic-size 会让滚动条在首滚时跳动；给首屏主视觉区域套 auto 会推迟用户最先看到的内容。打印与页内查找会强制渲染，这些流程仍要支付全量成本。

代码示例

/* Markup contract: each .form__field contains a label, an input,
   an optional .form__hint, and a .form__error paragraph. */

.form {
  display: grid;
  gap: var(--space-4, 1.5rem);
  max-inline-size: 32rem;
}

.form__field {
  display: grid;
  gap: var(--space-2, 0.5rem);
  border-radius: var(--radius-sm, 0.375rem);
}

.form__field > label {
  font-weight: 600;
}

.form__field input {
  font: inherit;
  padding-block: 0.5rem;
  padding-inline: 0.65rem;
  border: 1px solid var(--color-border, #a1a1aa);
  border-radius: var(--radius-sm, 0.375rem);
  background: var(--color-surface, #ffffff);
  color: var(--color-text, #18181b);
}

.form__error {
  display: none;
  margin: 0;
  font-size: 0.875rem;
  color: var(--color-danger, #b91c1c);
}

.form__field:has(input:required) > label::after {
  content: " *";
  color: var(--color-danger, #b91c1c);
}

.form__field:has(input:focus-visible) {
  outline: 2px solid var(--color-focus, #4f46e5);
  outline-offset: 4px;
}

/* :user-invalid appears only after the user has interacted or tried to submit. */
.form__field:has(input:user-invalid) input,
.form__field:has(input[aria-invalid="true"]) input {
  border-color: var(--color-danger, #b91c1c);
  background: var(--color-danger-surface, #fef2f2);
}

.form__field:has(input:user-invalid) .form__error,
.form__field:has(input[aria-invalid="true"]) .form__error {
  display: block;
}

@media (forced-colors: active) {
  .form__field:has(input:user-invalid) input,
  .form__field:has(input[aria-invalid="true"]) input {
    border: 2px solid Mark;
  }
}

/* Fallback without :has: use the general sibling combinator and show the
   message only for inputs explicitly marked invalid by script or server. */
@supports not selector(:has(*)) {
  .form__field input[aria-invalid="true"] {
    border-color: var(--color-danger, #b91c1c);
  }

  .form__field input[aria-invalid="true"] ~ .form__error {
    display: block;
  }
}

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Accessible confirmation dialog</title>
  <style>
    :root {
      color-scheme: light dark;
      font-family: system-ui, sans-serif;
    }

    body {
      margin: 0;
      padding: 2rem;
    }

    button {
      font: inherit;
      padding: 0.6rem 1rem;
      border: 1px solid currentColor;
      border-radius: 0.4rem;
      background: canvas;
      color: canvastext;
      cursor: pointer;
    }

    button:focus-visible {
      outline: 3px solid #4f46e5;
      outline-offset: 2px;
    }

    dialog {
      max-width: 32rem;
      border: 1px solid gray;
      border-radius: 0.75rem;
      padding: 1.5rem;
    }

    dialog::backdrop {
      background: rgb(0 0 0 / 55%);
    }

    .actions {
      display: flex;
      gap: 0.75rem;
      justify-content: flex-end;
      margin-top: 1.5rem;
    }
  </style>
</head>
<body>
  <main>
    <h1>Delete project</h1>
    <p>Deleting a project removes its deployments and environment variables.</p>
    <button type="button" id="open-dialog">Delete project…</button>
    <p id="status" role="status" aria-live="polite"></p>
  </main>

  <dialog id="confirm-dialog" aria-labelledby="dialog-title" aria-describedby="dialog-desc">
    <form method="dialog">
      <h2 id="dialog-title">Delete “Atlas”?</h2>
      <p id="dialog-desc">
        This permanently removes the project and its 12 deployments. This action cannot be undone.
      </p>
      <div class="actions">
        <button value="cancel" autofocus>Cancel</button>
        <button value="confirm">Delete permanently</button>
      </div>
    </form>
  </dialog>

  <script>
    const dialog = document.querySelector('#confirm-dialog');
    const openButton = document.querySelector('#open-dialog');
    const status = document.querySelector('#status');

    openButton.addEventListener('click', () => {
      dialog.returnValue = '';
      dialog.showModal();
    });

    dialog.addEventListener('close', () => {
      status.textContent = dialog.returnValue === 'confirm'
        ? 'Project deleted.'
        : 'Deletion cancelled.';
      openButton.focus();
    });

    dialog.addEventListener('click', (event) => {
      if (event.target === dialog) {
        dialog.close('cancel');
      }
    });
  </script>
</body>
</html>