<form>
    <label for="name">Name: <span class="req">*</span></label>
    <input name="name" type="text" required>

    <label for="birth">Date of Birth:</label>
    <input name="birth" type="date">

    <label for="origin">How did you find out about us? <span class="req">*</span></label>
    <select name="origin" required>
        <option>Google</option>
        <option>Facebook</option>
        <option>Advertisement</option>
    </select>
    <p><span class="req">*</span> - Required field</p>
</form>

label {
    display: block;
    margin-top: 1em;
}

.req {
    color: red;
}

*:optional {
    background-color: palegreen;
}