All CSS styles for HTML+CSS only form validation

style.css

body {
  background: linear-gradient(125deg, #9683EE, #3F4FDA);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  color: #65449B;
}

button {
  width: 150px;
  background: #65449B;
  color: white;
  font-family: 'Maven Pro', sans-serif;
  font-size: 1rem;
  padding: 1rem;
  border: none;
  border-radius: 5px;
  transition: all .5s cubic-bezier(0.075, 0.82, 0.165, 1);
  cursor: pointer;
}

button:hover {
  background: #392657;
}

.form {
  width: 500px;
  background: rgba(255, 255, 255, 1);
  border-radius: 20px;
  box-shadow: 0 0 20px #65449B;
  font-family: 'Overpass', sans-serif;
  overflow: hidden;
}

.form__header {
  font-family: 'Maven Pro', sans-serif;
  background: #65449B;
  color: white;
  margin: 0;
  padding: 1rem;
  text-align: center;
}

.form__field__error {
  color: #ff4d4d;
  margin: .25rem 0;
  font-size: .8rem;
  transition: all .5s cubic-bezier(0.075, 0.82, 0.165, 1);
  max-height: 0;
  opacity: 0;
}

.form__button {
  display: flex;
  justify-content: flex-end;
}

.form__content {
  padding: 2rem;
}

.form__field {
  position: relative;
  margin: 0 0 1rem;
  width: 100%;
}

.form__field__label {
  position: absolute;
  z-index: 0;
  top: .35rem;
  transition: all .5s cubic-bezier(0.075, 0.82, 0.165, 1);
}

.form__field__input {
  width: 100%;
  border: none;
  border-bottom: 1px solid #65449B;
  background-color: transparent;
  padding: .5rem 0;
  font-size: 1rem;
  position: relative;
  z-index: 1;
}

.form__field__state-icon {
  position: absolute;
  width: 1.5rem;
  height: 30px;
  right: .5rem;
  top: .25rem;
  background-repeat: no-repeat;
}

.form__field__input:invalid {
  border-bottom: 1px solid #ff4d4d;
}

.form__field__input:placeholder-shown {
  border-bottom: 1px solid #65449B;
}

.form__field__input:focus {
  outline: none;
}

.form__field__input:valid ~ .form__field__state-icon {
  background-image: url(/images/success.svg);
}

.form__field__input:invalid ~ .form__field__state-icon {
  background-image: url(/images/error.svg);
}
.form__field__input:placeholder-shown ~ .form__field__state-icon {
  background-image: url();
}

.form__field__input:invalid ~ .form__field__error {
  max-height: 40px;
  opacity: 1;
}
.form__field__input:placeholder-shown ~ .form__field__error {
  max-height: 0;
  opacity: 0;
}

.form__field__input:focus + .form__field__label,
.form__field__input:valid + .form__field__label,
.form__field__input:invalid + .form__field__label {
  top: -.5rem;
  font-size: .6rem;
}

.form__field__input:placeholder-shown + .form__field__label {
  top: .35rem;
  font-size: 1rem;
}