/* Важная часть */
.popup__bg {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100vh;
    background: rgba(0,0,0,0.5);
    opacity: 0;
    pointer-events: none; 
    transition: 0.5s all;
}

.popup__bg.active { 
    opacity: 1; 
    pointer-events: all;
    transition: 0.5s all;
}

.popup__popup {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%) scale(0); 
    background: #fff;
    width: 400px;
    padding: 25px;
    transition: 0.5s all;
}

.popup__popup.active { 
    transform: translate(-50%, -50%) scale(1);
    transition: 0.5s all;
}
/* Конец важной части */
/* Далее код для стилизации формы */
.close-popup {
    position: absolute;
    top: 10px;
    right: 10px;
    cursor: pointer;
    width: 25px;
}
.popup__popup h1{
    font-family: Arial, Helvetica, sans-serif;
    font-size: 20px;
}
.popup__popup p{
    font-family: Arial, Helvetica, sans-serif;
    line-height: 1.4rem;
}
span{
    color: red;
    font-weight: bold;
}
@media screen and (max-width: 425px){
    .popup__popup{
        max-width: 250px;
}
.popup__popup h1{
    font-family: Arial, Helvetica, sans-serif;
    font-size: 18px;
    text-align: center;
}
.popup__popup p{
    font-family: Arial, Helvetica, sans-serif;
    font-size: 13px;
    line-height: 1rem;
}
}