Эта строка в вашем коде является проблемой:
@media (min-width:767px) and (max-width: 576px){ ...
В вашем коде это относится ко всей ширине, превышающей 767, и ко всей ширине, меньшей 576 пикселей. Я полагаю, что это должно быть так:
@media (max-width:767px) and (min-width: 576px){ ...
... чтобы охватить ширину между 576 и 767px
ДОПОЛНЕНИЕ после комментариев:
Я добавил это (общее) правило:
.jumbotron img {
max-width: 100%;
}
В противном случае изображение внутри jumbotron будет иметь исходный размер, переполнение jumbotron при меньших размерах экрана, что также сделает всю страницу более широкой / заставляя полосу прокрутки.
body {
background-color: #fffffe;
}
.container {
margin: 0;
}
/** HEADER **/
#header-nav {
background-color: #5d46ea;
height: 78px;
border: 0;
}
#logo-img {
/** Logo **/
background: url(../images/imgonline-com-ua-resize-wU3umxGfKn8Y0H6h.jpg) no-repeat;
width: 150px;
height: 62px;
margin-left: 20px;
margin-right: 20px;
}
.navbar-brand h1 {
/** Blog Name **/
color: #fd9200;
font-family: 'oxygen', sans-serif;
font-size: 1.4em;
font-weight: bold;
text-transform: uppercase;
padding: 10px;
}
#nav-list a {
color: #fd9200;
font-weight: bold;
background: #5d46ea;
}
#nav-list a:hover {
background: #684fff;
}
.custom-toggler.navbar-toggler {
border: 1px solid rgb(253, 146, 0);
}
.navbar-light .navbar-toggler-icon {
background-image: url("data:image/svg+xml;charset=utf8,%3Csvg viewBox='0 0 30 30' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath stroke='rgba(253, 146, 0, 1)' stroke-width='2' stroke-linecap='round' stroke-miterlimit='10' d='M4 7h22M4 15h22M4 23h22'/%3E%3C/svg%3E");
}
/** HOME PAGE **/
.container {
margin-top: 10px;
}
.jumbotron {
background-color: #ffffff;
border: 2px solid #5d46ea;
box-shadow: 0 0 10px #5d46ea;
padding: 0;
margin: 0;
}
.jumbotron img {
max-width: 100%;
}
.row {
margin-top: 15px;
}
#main-tile,
#dessert-tile,
#smoothie-tile {
height: 250px;
width: 100%;
margin-bottom: 15px;
position: relative;
border: 2px solid #5d46ea;
box-shadow: 0 0 10px #5d46ea;
overflow: hidden;
}
#main-tile:hover,
#dessert-tile:hover,
#smoothie-tile:hover {
box-shadow: 0 1px 5px 1px #cccccc;
}
#main-tile {
background: url(https://via.placeholder.com/360x250) no-repeat;
background-position: center;
}
#dessert-tile {
background: url(https://via.placeholder.com/360x250) no-repeat;
background-position: center;
}
#smoothie-tile {
background: url(https://via.placeholder.com/360x250) no-repeat;
background-position: center;
}
#main-tile span,
#dessert-tile span,
#smoothie-tile span {
position: absolute;
bottom: 0;
right: 0;
width: 100%;
text-align: center;
font-size: 1.2em;
text-transform: uppercase;
background-color: #6a6a6a;
color: #fff;
opacity: .8;
}
/* END HOME PAGE */
/*************** MEDIA QUERIES ***************/
/** LARGE DEVICE **/
@media (min-width:1200px) {
.jumbotron {
background: url(https://via.placeholder.com/1200X675) no-repeat;
height: 675px;
}
}
/** MEDIUM DEVICE **/
@media (min-width:992px) and (max-width: 1199px) {
.jumbotron {
background: url(https://via.placeholder.com/992x558) no-repeat;
height: 558px;
}
}
/** SMALL DEVICE **/
@media (min-width: 768px) and (max-width: 991px) {
.jumbotron {
background: url(https://via.placeholder.com/768x432) no-repeat;
height: 432px;
}
}
/** EXTRA SMALL DEVICES **/
@media (max-width:767px) and (min-width: 576px) {
.jumbotron {
background: url(https://via.placeholder.com/768x432) no-repeat;
height: 432px;
}
#main-tile,
#dessert-tile,
#smoothie-tile {
width: 360px;
margin: 0 auto 15px;
}
}
/** SUPER EXTRA SMALL DEVICES **/
@media (max-width: 479px) {
#main-tile,
#dessert-tile,
#smoothie-tile {
width: 280px;
margin: 0 auto 15px;
}
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-witdth, initial-scale=1">
<title>Food Blog</title>
<link rel="stylesheet" href="css/bootstrap.min.css">
<link rel="stylesheet" href="css/bootstrap.css">
<link rel="stylesheet" href="css/styles.css">
</head>
<body>
<!-- HEADER -->
<header>
<nav id="header-nav" class="navbar navbar-light navbar-expand-lg">
<div class="navbar-header">
<a href="index.html" class="float-left d-none d-md-block">
<div id="logo-img" alt="Logo image"></div>
</a>
<div class="navbar-brand">
<a href="index.html">
<h1>Brand Name</h1>
</a>
</div>
</div>
<button class="navbar-toggler ml-auto custom-toggler" type="button" data-toggle="collapse" data-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarNav">
<ul id="nav-list" class="navbar-nav ml-auto text-center">
<li class="nav-item">
<a class="nav-link" href="#">Main</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Dessert</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Smoothie</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">About</a>
</li>
</ul>
</div>
</nav>
</header>
<!-- MAIN CONTENT -->
<div id="main-content" class="container mx-auto">
<!-- JUMBOTRON -->
<div class="jumbotron text-center">
<!-- FEATURED RECIPE -->
<img src="https://via.placeholder.com/768X432" alt="New Recipe Image" class="img-fluid d-block d-md-none">
</div>
<!-- TILES BELOW THE JUMBOTRON -->
<div id="home-tiles" class="row text-center">
<div class="col-md-4 col-sm-6 col-xs-12">
<a href="menu-categories.html">
<div id="main-tile"><span>Mains</span></div>
</a>
</div>
<div class="col-md-4 col-sm-6 col-xs-12">
<a href="menu-categories.html">
<div id="dessert-tile"><span>Deserts</span></div>
</a>
</div>
<div class="col-md-4 col-sm-12 col-xs-12">
<a href="menu-categories.html">
<div id="smoothie-tile"><span>Smoothies</span></div>
</a>
</div>
</div>
</div>
<!-- END OF MAIN CONTENT -->
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.4.1.slim.min.js" integrity="sha384-J6qa4849blE2+poT4WnyKhv5vZF5SrPo0iEjwBvKU7imGFAV0wwj1yYfoRSJoZ+n" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js" integrity="sha384-wfSDF2E50Y2D1uUdj0O3uMBJnjuUD4Ih7YwaYd1iqfktj0Uod8GCExl3Og8ifwB6" crossorigin="anonymous"></script>
</body>
</html>