@mixin tab-focus($shadow-color: get-color('primary', light)) {
    // WebKit-specific. Other browsers will keep their default outline style.
    // (Initially tried to also force default via `outline: initial`,
    // but that seems to erroneously remove the outline in Firefox altogether.)
    outline: none;
    box-shadow:
        1px 1px 0 $shadow-color,
        // bottom-right
        -1px 1px 0 $shadow-color,
        // bottom-left
        1px -1px 0 $shadow-color,
        // top-right
        -1px -1px 0 $shadow-color; // top-left
}