how to set height and width of image in css

Answer 1

img{
height:50%;
width:50%;
}
^^this in your css will change Every img object in your webpage.
if you make a class
.firstImg{
attributes
}
then assign it to one image it will style that individual image.

Answer 2

You can also Call them on only html file.. Example: <img src="image-name.jpg" height="200px" width="200px">