html, body, .container, form { padding: 0; height: 100%; }
.container { margin: 10px; }

.error {
    border: 2px solid red;
    margin-bottom: 10px;
}

textarea {
    width: 100%;
    height: 75%;
    padding: 10px;
    box-sizing: border-box;
    margin-bottom: 10px;
}

input[type="submit"] {
    margin-top: 10px;
    padding: 5px;
}