Align "Add to cart" buttons

Here’s how you would align these buttons if you’re using default WooCommerce styles. You could adjust the heights here as needed, and add this CSS to your child-theme stylesheet:

a.added_to_cart.wc-forward {
bottom: 0;
position: absolute;
display: block;
bottom: 0px;
}

.woocommerce ul.products li.product,
.woocommerce-page ul.products li.product {
min-height: 295px !important; /* <- modify the height of the gap here */
margin-bottom:10px;
}

a.button.add_to_cart_button,
a.button.product_type_simple {
bottom: 30px;
position: absolute;
}

 
Source: https://www.skyverge.com/blog/woocommerce-align-add-to-cart-buttons/