Edit in JSFiddle

<div class="block">Наведи сюда</div>

body {
  background: url('https://images.unsplash.com/photo-1445754574409-bcd715e18017?crop=entropy&fit=crop&fm=jpg&h=725&ixjsv=2.1.0&ixlib=rb-0.3.5&q=80&w=1325');
}

.block {
    width: 100px;
    height: 100px;
    background-color: #fff;
    display: inline-block;
    margin: 10px;
    line-height: 100px;
    text-align: center;
    font-size: 9pt;
    font-family: Verdana, Tahoma, sans-serif;
    cursor: pointer;
}
.block:hover,
.block:focus, 
.block:active {
  background-color: rgba(255, 255, 255, 0.5);
}