This Szczęśliwy icon is made in Material Design style developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 4,300 icons, all in the same style and quality.
There is a circle with medium bluntness of a line. There is a curved line in the bottom showing the mouth. There are two dots above the curved line showing the eyes. Both the line and dots are centered in the circle.