/* conceal dropdown in favor of autocomplete field in posts / pages */
tr.inline-edit-row td label select.authors.index-wp-users-for-speed {
    display: none;
}
/* conceal dropdown in favor of autocomplete field in classic editor */
div#authordiv.postbox > div.inside > select.index-wp-users-for-speed {
    display: none;
}
div#authordiv.postbox > div.inside > span.input-text-wrap > input.index-wp-users-for-speed {
    width:100%;
    max-width:40em;
}