static/css/add_product.css

.add{
    display: flex;
    flex-direction: column;
    margin:auto;
    width:400px;
    height:500px;
    padding:20px;
    padding-top: 20px;
    border: 7px solid blue;
    border-radius: 20px;
    margin-top: 50px;
}
.field{
    margin-bottom:10px;
}
button{
    border-radius: 20px;
    width: 70px;
    margin:auto;
    background-image: linear-gradient(45deg,greenyellow,blue);
    margin-top:10px;
}
body{
    background-color: aqua;
}