视觉上隐藏

使用 .visually-hidden 在视觉上隐藏元素，同时仍允许其暴露于辅助技术（例如屏幕阅读器）。默认情况下，使用 .visually-hidden-focusable 在视觉上隐藏元素，但在获得焦点时显示它（例如，由仅使用键盘的用户）。.visually-hidden-focusable 也可以应用于容器 - 感谢 :focus-within，当容器的任何子元素获得焦点时，容器就会被显示。

¥Visually hide an element while still allowing it to be exposed to assistive technologies (such as screen readers) with .visually-hidden. Use .visually-hidden-focusable to visually hide an element by default, but to display it when it’s focused (e.g. by a keyboard-only user). .visually-hidden-focusable can also be applied to a container–thanks to :focus-within, the container will be displayed when any child element of the container receives focus.

<h2 class="visually-hidden">Title for screen readers</h2>
<a class="visually-hidden-focusable" href="#content">Skip to main content</a>
<div class="visually-hidden-focusable">A container with a <a href="#">focusable element</a>.</div>

visually-hidden 和 visually-hidden-focusable 都可以用作 mixin。

¥Both visually-hidden and visually-hidden-focusable can also be used as mixins.

// Usage as a mixin

.visually-hidden-title {
  @include visually-hidden;
}

.skip-navigation {
  @include visually-hidden-focusable;
}