Hello,
Welcome to the shopify Community.
Please remove old given code.
Please Go to Online Store → Themes → Edit code → Assets → theme.scss.liquid and paste this code at the end of this file.
#shopify-section-collection .page-width .grid .grid__item {
position: relative;
min-height: 450px;
}
#shopify-section-collection .page-width .grid .grid__item form {
position: absolute;
bottom: 0px;
margin-bottom: 15px;
}
@media only screen and (max-width: 768px) {
#shopify-section-collection .page-width .grid .grid__item {
min-height: 350px;
}