#postSignupForm {
    display: flex;
    align-items: stretch;
    width: 100%;
}

#postSignupForm input {
    width: 100%;
}

.post-signup-message {
    max-height: 0px;
    overflow: hidden;
    transition: all .5s ease-in-out;
}

.post-signup-message.active {
    max-height: 100px;
}