.error form input[type="text"]{
    box-shadow: 0 0 1em red;
    -webkit-box-shadow: 0 0 1em red;
    -o-box-shadow: 0 0 1em red;
    -moz-box-shadow: 0 0 1em red;
}

.error3 input[type="password"]{
    box-shadow: 0 0 1em red;
    -webkit-box-shadow: 0 0 1em red;
    -o-box-shadow: 0 0 1em red;
    -moz-box-shadow: 0 0 1em red;
}

$errors = array();
        if (empty($Username)) { array_push($errors, "Username is required"); }


if ($Password_1 != $Password_2) {
            array_push($errors, "<div class='error3'>Password isn't the same.</div>");
        }

<?php include('includes/errors.php'); ?>
    <div class="form-group">

                            <label for="Password_2">Verify password</label>
                            <div class="input-icon">
                                <i class="mdi mdi-lock"></i>
                                <span class="passtoggle mdi mdi-eye toggle-password"></span>
                                <input type="password" class="form-control" id="password" name="Password_2"
                                       placeholder="Verify password" required>
                            </div>
                        </div>