.t-form__screen .t-form__screen-btn-next::after {
    content: ''!important;
    background: url('https://mostpp.ru/arrow.svg');
    position: absolute;
width: 17px;
height: 17px;
z-index: 999999999;
background-size: contain;
right: 7px;
top: 14px;
}

.t-form__screen .t-form__screen-btn-prev::before {
     content: ''!important;
    background: url('https://mostpp.ru/arrow.svg');
    position: absolute;
    width: 17px;
    height: 17px;
    z-index: 999999999;
    background-size: contain;
    left: 7px;
    top: 14px;
    transform: rotate(180deg);
}