Visually hidden to sighted users. Still able to be read by screen readers.

visually-hidden.css

/*
 * Hide only visually, but have it available for screen readers:
 * https://snook.ca/archives/html_and_css/hiding-content-for-accessibility
 *
 * 1. For long content, line feeds are not interpreted as spaces and small width
 *    causes content to wrap 1 word per line:
 *    https://medium.com/@jessebeach/beware-smushed-off-screen-accessible-text-5952a4c2cbfe
 */

.visuallyhidden {
    border: 0;
    clip: rect(0 0 0 0);
    height: 1px;
    margin: -1px;
    overflow: hidden;
    padding: 0;
    position: absolute;
    width: 1px;
    white-space: nowrap; /* 1 */
}

/*
 * Extends the .visuallyhidden class to allow the element
 * to be focusable when navigated to via the keyboard:
 * https://www.drupal.org/node/897638
 */

.visuallyhidden.focusable:active,
.visuallyhidden.focusable:focus {
    clip: auto;
    height: auto;
    margin: 0;
    overflow: visible;
    position: static;
    width: auto;
    white-space: inherit;
}