Hi Ivan,
So here is the current menu-toggle CSS, its using a before pseudo element, so you can change the unicode and font family if you want to use font icons:
.menu-toggle:before {
content: "\f0c9";
font-family: GeneratePress;
width: 1.28571429em;
text-align: center;
display: inline-block;
}
The Content property can support an image like so: content: url(image.jpg);
You can use this filter to change the shopping cart icon, note: GP 1.7 comes with a few icon choices:
https://docs.generatepress.com/article/generate_woocommerce_menu_cart_icon/