.newsletter-signup-form ::-webkit-input-placeholder {
    color: black !important;
    opacity: 1;
}
.newsletter-signup-form input[type="email"]:focus::-webkit-input-placeholder {
    color:white !important;
}
.newsletter-signup-form input[type="email"]{
    background: white;
    color: #000000;
    border-color: white;
}
.newsletter-signup-form input[type="email"]:focus {
    border-color: black;
}
.newsletter-signup-form .hs-error-msg {
    color: #ffffff !important;
}
.newsletter-signup-form form .hs-richtext, .newsletter-signup-form form .hs-richtext p, .newsletter-signup-form form .hs-richtext a {
    color: white;
}
.newsletter-signup-form .actions {
    margin-top: 4px;
}
.newsletter-signup-form .actions input {
    height: 42px;
}
.newsletter-signup-inner .hs_email {
    flex-grow: 1;
}
.newsletter-signup-inner {
    margin-bottom: 4px;
}
.newsletter-signup-form  .submitted-message {
    color: white;
}
@media (min-width: 992px){
    .newsletter-squircle {
        position: absolute;
    }
}
<style>
@media (max-width: 767px) {

  .hs-submit {
    display: flex !important;
    justify-content: center !important;
    width: 100% !important;
  }

  .hs-submit .hs-button {
    margin: 0 !important;
  }

}
</style>