Make a radial gradients radius 200px

Question

How would I make the radius 200px in width and height? I've read that this can be done in pixel units, but every attempt has failed.

background-image: -webkit-radial-gradient(75% 100%, circle farthest-corner, #ffffff, #ff7ae9 33%);
background-image: -o-radial-gradient(75% 19%, circle farthest-corner, #ffffff, #ff7ae9 33%);
background-image: -ms-radial-gradient(75% 19%, circle farthest-corner, #ffffff, #ff7ae9 33%);
background-image: radial-gradient(75% 19%, circle farthest-corner, #ffffff, #ff7ae9 33%)
background-image: -moz-radial-gradient(75% 19%, circle farthest-corner, #ffffff, #ff7ae9 33%);

Answer 1

edit: added all the vendor prefixes to make it clearer

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background-image:    -moz-radial-gradient(50px 100px, circle farthest-corner, #ffffff, #ff7ae9 200px);
background-image: -webkit-radial-gradient(50px 100px, circle farthest-corner, #ffffff, #ff7ae9 200px);
background-image:      -o-radial-gradient(50px 100px, circle farthest-corner, #ffffff, #ff7ae9 200px);
background-image:     -ms-radial-gradient(50px 100px, circle farthest-corner, #ffffff, #ff7ae9 200px);
background-image:         radial-gradient(50px 100px, circle farthest-corner, #ffffff, #ff7ae9 200px);

In this example the '200px' is the size of the circle, any standard CSS units such as px, em or percentages are fine.

The '50px 100px' is the position of the centre of the circle, it works the same way as background-position so values like 'left top' are fine too.

There are a few online generators that can help you with all the vendor specific prefixes.

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p.s.
@Mohsen pixel values are fine, MDN says:

either a percentage between 0% and 100% or a length along the gradient axis

If you click on 'length' it says

The CSS syntax for length is a number followed immediately by a unit. Space between the number and the unit is not allowed.