Hello,
1) Here is the custom CSS code:
.widget_product_categories.sidebar-widget ul > li {
border-bottom: 1px solid black;
}
2)
.single-product .product-content .product_title {
margin-bottom: 2vw;
}
3) Please describe the desired result in more details.
4) Every page can have only 1 sidebar. Content of the Single product sidebar can be changed via Appearance > Widgets, the position of the sidebar > Theme Options > WooCommerce (Shop) > Single product page > Single product layout.
Regards