Add VisuallyHidden atom component

admin/src/components/atoms/VisuallyHidden.tsx

@@ -0,0 +1,16 @@
+import styled from '@emotion/styled';
+
+/** A component which hides its children. The children will still be available for screen readers.
+ * @see {@link https://www.a11yproject.com/posts/how-to-hide-content/} for further information.
+ */
+const VisuallyHidden = styled.span`
+  clip: rect(0 0 0 0);
+  clip-path: inset(50%);
+  height: 1px;
+  overflow: hidden;
+  position: absolute;
+  white-space: nowrap;
+  width: 1px;
+`;
+
+export default VisuallyHidden;