.simple-checkbox {
    display: none;
}

.simple-checkbox + span {
    width: 16px;
    display: inline-block;
}

.simple-checkbox + span:before {
    border: 1px solid #333;
    content: "\00a0";
    display: inline-block;
    font: 16px/1em sans-serif;
    height: 16px;
    margin: 0 0.25em 0 0;
    padding: 0;
    vertical-align: top;
    width: 16px;
    padding-bottom: 2px;
}

.simple-checkbox:checked + span:before {
    border-color: transparent;
    background: #29f;
    color: #fff;
    content: "\2713";
    font-size: 1.3em;
    text-align: center;
}

.simple-checkbox:checked + span:after {
    font-weight: bold;
}