Grouped Form with Fieldsets

<!DOCTYPE html>
<title>My Example</title>

.form-group {
    margin-bottom: 15px;
}
.form-group label {
    display: block;
    margin-bottom: 5px;
    font-weight: 500;
}
.form-group input {
    width: 100%;
    padding: 10px;
    border: 1px solid #ccc;
    border-radius: 4px;
    font-size: 1rem;
    box-sizing: border-box;
}

.submit-btn {
    width: 100%;
    padding: 12px;
    border: none;
    background-color: #007bff;
    color: white;
    font-size: 1.1rem;
    font-weight: bold;
    border-radius: 5px;
    cursor: pointer;
}
</style>

<div class="fieldset-form-container">
    <form action="#" method="post">
        <h2>Account Profile</h2>
    
        <fieldset>
            <legend>User Identity</legend>
            <div class="form-group">
                <label for="username">Username</label>
                <input type="text" id="username" name="username">
            </div>
            <div class="form-group">
                <label for="email">Email Address</label>
                <input type="email" id="email" name="email">
            </div>
        </fieldset>
    
        <fieldset>
            <legend>Security</legend>
            <div class="form-group">
                <label for="current-password">Current Password</label>
                <input type="password" id="current-password" name="current_password">
            </div>
            <div class="form-group">
                <label for="new-password">New Password</label>
                <input type="password" id="new-password" name="new_password">
            </div>
        </fieldset>
        
        <fieldset>
            <legend>Contact Information</legend>
             <div class="form-group">
                <label for="phone">Phone Number</label>
                <input type="tel" id="phone" name="phone">
            </div>
             <div class="form-group">
                <label for="address">Mailing Address</label>
                <input type="text" id="address" name="address">
            </div>
        </fieldset>
        
        <button type="submit" class="submit-btn">Save Changes</button>
    </form>
</div>