Просто оберните ваши входы в div:
$().ready(function() {
// validate the comment form when it is submitted
$("#commentForm").validate();
// validate signup form on keyup and submit
$("#signupForm").validate({
rules: {
fname: "required",
lname: "required",
password: {
required: true,
minlength: 8
},
cpassword: {
required: true,
minlength: 8,
equalTo: "#password"
},
email: {
required: true,
email: true
},
topic: {
required: "#newsletter:checked",
minlength: 2
},
agree: "required"
},
messages: {
firstname: "Your first name is required.",
lastname: "Please enter your lastname",
username: {
required: "Please enter a username",
minlength: "Your username must consist of at least 2 characters"
},
password: {
required: "Please provide a password",
minlength: "Your password must be at least 8 characters long"
},
cpassword: {
required: "Please provide a password",
minlength: "Your password must be at least 8 characters long",
equalTo: "Please enter the same password as above"
},
email: "Please enter a valid email address",
}
});
});
* {
box-sizing:border-box;
}
input[type="text"],
input[type="email"],
input[type="password"] {
padding: 4px 20px;
height: 35px;
border: 1px solid black;
border-radius: 3px;
width:100%;
}
.form-row {
flex-direction: row;
display: flex;
}
.form-row > div {
margin: 10px;
flex-grow:1;
}
.form-panel {
margin-left: auto;
margin-right: auto;
width: 60%;
}
input {
display: block;
}
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="//code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/jquery-validation@1.17.0/dist/jquery.validate.js"></script>
<style>
</style>
</head>
<body>
<form class="form-panel" id="signupForm">
<div class="form-row form-name">
<div><input type="text" name="fname" placeholder="First Name"></div>
<div><input type="text" name="lname" placeholder="Last Name"></div>
</div>
<div class="form-row form-email">
<div><input type="email" name="email" placeholder="Email Address"></div>
</div>
<div class="form-row form-password">
<div><input type="password" name="password" placeholder="Password"></div>
<div><input type="password" name="cpassword" placeholder="Comfirm Password"></div>
</div>
<input type="submit" class="btn btn-default submit-button" value="Sign up!">
</form>
<script>
</script>
</body>
</html>