Increase font size in WordPress post and page editor..

Hi all.
I need is to increase the font size ONLY in the posts/page editor (ie page-wide) as my eyesight is bad. Anyone know how to do this? For some reason the text in wp-admin page editor is always tiny – whist the actual viewed page is large (the size I want – so increasing browser size does not help as then it gets too big on the when I have both edit page and viewed page in 2 browser windows)

Any help very much welcome
Thanks.