#fkey_prefs_selector {
    position: absolute;
    top: 0px;
    left: 0px;
    width: 16px;
    border-width: 2px;
    border-style: solid;
    box-sizing: border-box;
    animation: blink 0.3s steps(1, end) infinite;
    pointer-events: none;
}

@keyframes blink {
    0% {border-color: white;} 50% {opacity: 0;}
}