Problem with smooth-scroll

<nav id="navbar-follow" class="navbar navbar-expand-sm fixed-top navbar-dark flex-nowrap" style="background-color:#222;">

<divclass="navbar-collapse collapse">

<ulclass="smooth-scroll navbar-nav nav-pills mx-auto ">

<liclass="nav-item">

<ahref="#services"class="nav-link">Services</a>

</li>

<liclass="nav-item">

<ahref="#portfolio"class="nav-link nav-outline-success">Portfolio</a>

</li>

<liclass="nav-item">

<ahref="#about"class="nav-link">About</a>

</li>

<liclass="nav-item">

<ahref="#contact"class="nav-link">Contact</a>

</li>

</ul>

</div>

</nav>

<div data-spy="scroll" data-target="navbar-follow" data-offset="0">

<header>

<divclass="container">

<divclass="intro-text">

<divclass="intro-lead-in">...</div>

<divclass="intro-heading">...</div>

</div>

</header>



<section id="services">...</section>

<section id="portfolio">...</section>

<section id="about">...</section>

<section id="contact">...</section>

</div>