Keyboard-only focus styles

**** HTML
** Important: add tabindex="-1" to child tag
<button id="btn" class="btn" type="button">
    <span class="btn__content" tabindex="-1">
        I'm a button!
    </span>
</button>

<a class="btn" href="#x">
    <span class="btn__content" tabindex="-1">
        I'm a link!
    </span>
</a>

<span class="btn" tabindex="0">
    <span class="btn__content" tabindex="-1">
        I'm a span!
    </span>
</span>

**** CSS:

/* All the states on the inner element */
.btn:hover > .btn__content  {
    background: salmon;
}

.btn:active > .btn__content  {
    background: darkorange;
}

.btn:focus > .btn__content  {
    box-shadow: 0 0 2px 2px #51a7e8;
    color: lime;
}

/* Removing default outline only after we've added our custom one */
.btn:focus,
.btn__content:focus {
    outline: none;
}