Usually this message appears when your web browser's zoom setting is something other than 100%.
Why? : When you increase/decrease your zoom you also increase/decrease the size of elements on your page. So a 1px line might now be 3px.
What to do? : Often, resetting zoom to default will do the trick. You can reset it with cmd-0 (Mac) or ctrl-0 (PC).
You may need to experiment to get it right with your browser:
- Some people have reported that Firefox likes 80% zoom to give the right answer.
- "I'm on Firefox and a Surface Pro 3; the resolution is so high that they shift the default zoom (ctrl-0) to improve readability. Ctrl+(-) ×3 "fixed" it."
- in Safari, uncheck never use a font size smaller than.... ( thanks jrjinaustin )
- I set to 67% zoom on firefox after experimenting for awhile & it finally worked. (thanks @sheilacm)