TO Increase Perfomance :

We have to mainitain image size less
We have to write css less like ( we can'nt write inline css and we can't write in Html files. )
we have to write external css.
which image size, we can compress jpeg images
we have to maintain images size in Kbs
Same image we have to use for mobile and desktop and tablets.
so many people user different images for desktop and mobiles.
same image with different size but we have to use
same images and we have to adjust the size , dont use different size of images , loading will be decrease.