<div class="popup-subscribe__box popup-subscribe__box-name">
<label class="popup-subscribe__label" for="popup-subscribe__name">Enter your name</label>
<input class="popup-subscribe__input" id="popup-subscribe__name" type="text" name="Name" placeholder="Anastasiia" required>
<span></span>
</div>
span {
position: relative;
}
span::after {
content: "+";
position: absolute;
top: 0;
right: 17px;
transition: all ease-in 0.3s;
transform: scale(0);
background-color: #1ED760;
}
.popup-subscribe__input:valid + span::after {
transform: scale(1);
}
.title:hover ~ .title::after {
transform: rotate(180deg);
}
<element>:hover::after { /* ... style */ }
.title:hover::after {
transform: rotate(180deg);
}