.t-checkbox__indicator::after{
    content: "✓" !important;

    color: #fff !important;
    font-size: 18px !important;
    font-weight: 700 !important;
    line-height: 22px !important;

    position: absolute !important;
    left: 3px !important;
    top: -2px !important;

    opacity: 0 !important;
}

.t-checkbox:checked + .t-checkbox__indicator::after{
    opacity: 1 !important;
}