Hello,
Add the next code in Theme Options > Theme custom CSS:
.woocommerce-order-received .woocommerce-order-overview-wrapper ~ p {
background-color: #32ab2f;
}
.woocommerce-order-received .woocommerce-order-overview li strong,
.woocommerce-order-received .shop_table .amount,
.woocommerce-order-received .wc-item-meta li{
color: #555;
}
Regards