100% width background image with an 'auto' height

Question

I\'m currently working on a mobile landing page for a company. It\'s a really basic layout but below the header there\'s an image of a product which will always be 100% widt

Answer 1

html{
    height:100%;
    }
.bg-img {
    background: url(image.jpg) no-repeat center top; 
    background-size: cover; 
    height:100vh;     
}