When you create a button with an icon type, the icon is not centered, but 4 pixels to the left.
Button with an iconButton type should be with left padding, because this type is used with a label which is right of the icon. The icon type is also can be used with a label.
If you need only an icon, so please use view:"icon"
Or you can center the icon with the help of CSS in the sample which you sent
Like this: https://snippet.webix.com/0qvehi85
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