.contact-form {
display: flex;
flex-direction: column;
}

.contact-form__row {
display: flex;
flex-direction: column;
}

.contact-form__input {
flex-grow: 1;
border: 1px solid rgb(169, 169, 169);
padding: .5em 1em;
margin-top: 16px;
}

.contact-form__main-input {
margin-top: 16px;
padding: .5em 1em;
font-family: Arial, “Helvetica Neue”, Helvetica, sans-serif;
resize: none;
height: 8em;
}

.contact-form__submit {
align-self: flex-end;
margin-top: 16px;
height: 32px;
font-family: inherit;
font-size: 11px;
color: #fff;
background-color: #59ed89;
text-transform: uppercase;
text-align: center;
font-weight: 600;
cursor: pointer;
border: 0;
padding: 0 16px;
transition: background .17s ease;
}

.contact-form__submit:hover {
background-color: #111111;
}

@media (min-width: 600px) {

.contact-form__row {
flex-direction: row;
}

.contact-form__input {
margin-top: 16px;
}

.contact-form__input:not(:first-child) {
margin-left: 16px;
}
}

Seu elogio, sugestão ou crítica são bem-vindos!