Contact Form 7 - Customizar mensagens de erros

contact-form7.css

body input[type=text].wpcf7-not-valid,
body input[type=email].wpcf7-not-valid,
body input[type=tel].wpcf7-not-valid,
body textarea.wpcf7-not-valid {
	border: 1px solid #ec3c06;
}

body span.wpcf7-not-valid-tip {
	background: none;
	border: none;
	color: #ec3c06;
	display: block;
	font-size: 15px;
	left: auto;
	margin-top: 2px;
	padding: 0;
	position: relative;
	top: auto;
}

body div.wpcf7-validation-errors {
	background: #ffe2e2;
	border: 1px solid #ff8a8a;
	color: #ec3c06;
}

body div.wpcf7-response-output {
	box-sizing: border-box;
	-webkit-box-sizing: border-box;
	-moz-box-sizing: border-box;
	border-radius: 5px;
	margin: 10px 0;
	padding: 20px;
}

body .wpcf7-mail-sent-ng {
	background: #fff2e2;
	border: 1px solid #ffbc8a;
	color: #e17731;
}

body .wpcf7-mail-sent-ok {
	background: #e8ffe2;
	border: 1px solid #6fdf51;
	color: #1ea524;
}

.wpcf7-captchac {
	border: 1px solid #dee1e1;
	margin-bottom: 10px;
	padding: 20px 40px;
}

contact-form7.scss

body {
	input[type=text].wpcf7-not-valid,
	input[type=email].wpcf7-not-valid,
	input[type=tel].wpcf7-not-valid,
	textarea.wpcf7-not-valid {
		border: 1px solid #ec3c06;
	}

	span.wpcf7-not-valid-tip {
		background: none;
		border: none;
		color: #ec3c06;
		display: block;
		font-size: 15px;
		left: auto;
		margin-top: 2px;
		padding: 0;
		position: relative;
		top: auto;
	}

	div.wpcf7-validation-errors {
		background: #ffe2e2;
		border: 1px solid #ff8a8a;
		color: #ec3c06;
	}

	div.wpcf7-response-output {
		box-sizing: border-box;
		@include box-sizing (border-box);
		border-radius: 5px;
		margin: 10px 0;
		padding: 20px;
	}

	.wpcf7-mail-sent-ng {
		background: #fff2e2;
		border: 1px solid #ffbc8a;
		color: #e17731;
	}

	.wpcf7-mail-sent-ok {
		background: #e8ffe2;
		border: 1px solid #6fdf51;
		color: #1ea524;
	}

	.wpcf7-captchac {
		border: 1px solid #dee1e1;
		margin-bottom: 10px;
		padding: 20px 40px;
	}
}