I use his code now and it seems to work for me:
.product-image {
height: 200px;
float: none !important;
/* display: inline-block !important; */
vertical-align: middle !important;
position: relative;
margin: 1em 0;
/* background: white; */
}
.woocommerce ul.products li.product a img, .woocommerce-page ul.products li.product a img {
/* width: auto !important; */
/* max-height: 300px !important; */
/* margin-left: auto !important; */
/* margin-right: auto !important; */
position: absolute;
margin: auto;
max-width: 150px;
max-height: 150px;
top: 0;
right: 0;
bottom: 0;
left: 0;
width: auto;
}