A light smile means you are satisfied with yourself and the world. Can make a statement sound friendlier than it might have been meant. Or have a sarcastic meaning when a smile does not actually fit the content.
The slightly smiling face emoji was introduced in 2014 and released as part of the Unicode 11.0 standard. This emoji can be found under the smileys and emotions
category. Because the slightly smiling face emoji has been around for quite some time, it should display correctly in the majority of operating systems.