Is it just in my installation or overall that ribbon
Configure and button
Icon are behaving incorrectly on Chrome and Firefox in
Sitecore 9 Update 1?
Dialog box is hidden behind content tree:
I need to scroll toolbar down to get to More Icons button:
UPDATE: Bug reported to Sitecore Support and it is tracked with reference number 202331. Ask Sitecore Support to provide fix, it is working as expected after applying update package ;)
WORKAROUND: I have summarized Vlad's suggestions + my own findings on various ways how to change icons in Sitecore in a blog post.
Take a look here -> https://tothecore.sk/2018/02/14/various-ways-of-changing-item-icons-in-sitecore/