Red outline indicating validation error on text inputs is hidden

system.theme.css

.form-item input.error, .form-item textarea.error, .form-item select.error {
    border: 2px solid red;
}

is overridden by Sky css/form.css

input.form-text, select[multiple="multiple"] {
    border: 2px solid #E6E4DE !important;
}

This causes the red outline used to signify a text-input validation error (e.g., leaving a required field empty) to be hidden. So the user has no visual indication of which text inputs have errors.