Responsive images - resolution switchingApproved

Use `srcset` attribute in the `` tag when you need to select a different source of the same image because you need a different resolution. The height and width of the image should remain fixed. ```html

``` Сustom height and width of the image based on the viewport. ````html

```` Also see demo page [here](https://scottjehl.github.io/picturefill/examples/demo-01.html)