nathan111777,
перенесите строки 8 - 34 в ваш файл style.css и добавьте тег <link rel="stylesheet" href="css/style.css">
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.single-goods {
width: 22%;
max-width: 300px;
border: 1px solid black;
text-align: center;
display: flex;
flex-direction: column;
justify-content: center;
}
.single-goods button {
height: 2em;
}
.single-goods img{
width: 100%;
height: auto;
}
.single-goods *{
margin: 0;
}
.single-goods p{
margin: 2px 0px;
}
#goods {
display: flex;
flex-wrap: wrap;
justify-content: space-around;
}
</style>
</head>
<body>
<div id="goods"><div class="single-goods"><h3>Платье1</h3><p>Цена: 50</p><img src="https://cdn.shopify.com/s/files/1/2671/4680/products/pol_dress_sage_240x.jpg?v=1553634712"><button class="add-to-cart" data-art="11292">Купить</button></div><div class="single-goods"><h3>Платье2</h3><p>Цена: 150</p><img src="https://cdn.shopify.com/s/files/1/0519/8561/products/IMG_5881_76665333-5efd-46da-b57e-2472ddb55697_240x.jpg?v=1548397696"><button class="add-to-cart" data-art="11294">Купить</button></div><div class="single-goods"><h3>Платье3</h3><p>Цена: 200</p><img src="https://cdn.shopify.com/s/files/1/0073/5671/1030/products/websizedphotos_1_copy_6_522fb324-3529-4e22-989e-0924860cb34d_240x.png?v=1553665976"><button class="add-to-cart" data-art="11295">Купить</button></div><div class="single-goods"><h3>Платье4</h3><p>Цена: 300</p><img src="https://cdn.shoptiques.com/shoptiques-shop/products/mock-neck-dress-14-blue-9f38a7d3_pl.jpg"><button class="add-to-cart" data-art="11296">Купить</button></div></div>
</body>
</html>