Have you considered using a simpler code without Bootstrap? Here's an example:
.buger {
margin-left: auto;
display: none;
}
.buger div {
width: 20px;
border-top: 3px solid #454545;
padding-bottom: 3px;
}
.flex {
display: flex;
}
@media (max-width: 576px) {
.buger {
display: block;
}
.menu {
display: none;
}
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8>
<meta name="viewport" content="width=device-width, initial-scale=1.0>
<title>Document</title>
</head>
<body>
<div class="flex>
<nav class="menu>
<a href="">Menu 1</a>
<a href="">Menu 2</a>
<a href="">Menu 3</a>
</nav>
<div class="buger>
<div class="line-1></div>
<div class="line-2></div>
<div class="line-3></div>
</div>
</div>
</body>
</html>