.checkbox {
    position: absolute;
    left: 0;
    top: 3px;
    display: block;
    width: 20px;
    height: 20px;
    border: #fff 2px solid;
    opacity: .2;
}

.contacts__personal-data input:checked ~ .checkbox {
    opacity: 1;
    background-image: url(../../images/checkbox-on.svg);
    background-repeat: no-repeat;
    background-size: 10px 10px;
    background-position: 3px 3px;
    border: #fff 2px solid;
}