External css import, url replaced

.navbar-dark .navbar-toggler-icon {
    background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' width='30' height='30' viewBox='0 0 30 30'%3e%3cpath stroke='rgba%28255, 255, 255, 0.5%29' stroke-linecap='round' stroke-miterlimit='10' stroke-width='2' d='M4 7h22M4 15h22M4 23h22'/%3e%3c/svg%3e");
}

Try and paste this code in anywhere…its the Bootstrap 4 Hamburger

Ok so, I’ve narrowed it down to the Double Quotes inside the brackets. If you remove those, the code goes in fine. BTW, what is he…iterlimit ?