How can I make the website responsive,

Replace <h2> with <h1> to fix the accessibility issue.

Always begin the heading of the html with <h1> tag because the <h1> is needed to make the content accessible, wrap the sub-heading of <h1> in <h2> tag, wrap the sub-heading of <h2> in <h3> this continues until <h6>, never skip a level of a heading.

Give the alt attribute in the img a value. The value of the alt attribute is the description of the image. For decorative images like icons, there is no need to give it an alt value, for more on alt attribute Click here.

To center .product-container on the page, using flexbox, replace the height in .main-container with min-height:100vh

Use relative units like rem or em as unit for the padding, margin, width values and preferably rem for the font-size values, instead of using px which is an absolute unit. For more on CSS units Click here

Hope am helpful.

Well done for completing this challenge. HAPPY CODING