.keyboard {
    text-align: center;
    margin: 0;
    display: none;
}

.keyboard-row {
    margin: 5px;
}

.keyboard-button {
    display: inline-block;
    width: 8.5%;
    line-height: 0;
    font-size: 16px;
    border-radius: 3px;
    border: 1px solid #777;
    position: relative;
}

.keyboard-button:after {
  content: "";
  display: block;
  padding-bottom: 100%;
}

.keyboard-button:before {
    content: attr(value);
    position: absolute;
    top: 50%;
    left: 0;
    width: 100%;
    display: inline-block;
    text-align: center;
}