create background cover image

hello, how to background cover image like this website? parsaya.com
i want to use this css for my website.
thanks

html code

Code:

---

<img src="img.png" class="responsive-image">

---

put the name your image whatever it is in that bolded part

css code

Code:

---

.responsive-image{
    width: 100%;
    background-size: 100% 100%;
}

and finally, we serve for every view-port the right image:

/* Retina display */
@media screen and (min-width: 1024px){
    .responsive-image{
        background-image: url('../img/retina.jpg');
    }
}

/* Desktop */
@media screen and (min-width: 980px) and (max-width: 1024px){
    .responsive-image{
        background-image: url('../img/desktop.jpg');
    }
}

/* Tablet */
@media screen and (min-width: 760px) and (max-width: 980px){
    .responsive-image{
        background-image: url('../img/tablet.jpg');
    }
}

/* Mobile HD */
@media screen and (min-width: 350px) and (max-width: 760px){
    .responsive-image{
        background-image: url('../img/mobile-hd.jpg');
    }
}

/* Mobile LD */
@media screen and (max-width: 350px){
    .responsive-image{
        background-image: url('../img/mobile-ld.jpg');
    }
}

---