JSFiddle - React, Tailwind, and code Playground

by Sergei

HTML

<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8" />
    <!-- <meta http-equiv="X-UA-Compatible" content="IE=edge"> -->
    <title>Page Title</title>
    <!-- <meta name="viewport" content="width=device-width, initial-scale=1"> -->
    <link href="main.css" rel="stylesheet">
</head>

<body>
    <form action="#" class="form">
        <div class="form__field">
            <input type="text" name="name" placeholder="Имя*" required />
        </div>
        <div class="form__field">
            <input type="email" name="name" placeholder="E-Mail" />
            <span class="form__error">Это поле должно содержать E-Mail в формате [email protected]</span>
        </div>
        <button type="submit form__error" id="">Отправить</button>
    </form>
</body>

</html>

CSS

body {
  text-align: center;
  padding: 10px;
}

.form {
  display: inline-block;
  padding: 25px;
  border: 1px solid #ccc;
  border-radius: 5px;
  width: 500px;
  background-color: beige;
}

.form__field {
  margin-bottom: 10px;
}

.form__error {
  color: red;
  text-align: left;
  font-size: 12px;
  display: block;
  margin-top: 3px;
  display: none;
}

.form input {
  outline: none;
  display: block;
  width: 100%;
  border-radius: 2px;
  border: 1px solid #ccc;
  padding: 10px;
  box-sizing: border-box;
}

.form button {
  width: 100%;
  padding: 10px;
  border-radius: 2px;
  border: 0;
  background-color: #ccc;
  color: #fff;
}

input:valid:not(:placeholder-shown) {
  border-color: green;
}
 button:valid:not(:placeholder-shown) {
  border-color: green;
}

input:invalid:not(:placeholder-shown) {
  border-color: red;
}

input:invalid:not(:placeholder-shown) + .form__error {
  display: block;
}