Product preview card component with HTML5 , CSS, Flexbox, Bootstrap 4

Hi Larisa! Congratulations on completing this challenge... There are several better ways to center the card, I personally recommend using the position: absolute method:

main{
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

I also suggest you use a more semantic HTML, you can use <main>, <section> or <article> etc.