My web page's top div spills out of its space and overlaps another part of the screen when viewed on tablets or mobile devices. I am using bootstrap grids, but it seems like I might be doing something wrong. Any assistance would be greatly appreciated.
Screenshot showing correct placement on a desktop PC
Screenshot showing incorrect placement on an iPhone
<div class="container mt-5">
<div class="row no gutters header text-left mt-5">
<div class="col-sm-12">
<h1 id="testing-1" class="display-4 text-left">Digital Study Skills Tutor</h1>
<p class="lead">Free self-help study skills resources for university students</p>
<a class="btn btn-lg btn-primary" href="signup.php">Sign Up</a>
</div>
</div>
</div>
.site-header {
background: url(img/home-header.jpg) no-repeat center;
background-size: cover;
}
.site-header .layout-hero {
min-height: 100vh;
}
.display-4 {
font-size: 2.25em;
font-weight: 500;
color: white;
}