.bootstrap-checkbox {
    display:inline-block;
    position:relative;
    width:13px;
    height:13px;
    border:1px solid #000;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}

.bootstrap-checkbox i{
    position:absolute;
    left : -1px;
    top : -2px;
}