The sin() CSS function is a trigonometric function that returns the sine of a number, which is a value between -1 and 1. The function contains a single calculation that must resolve to either a <number> or an <angle> by interpreting the result of the argument as radians. That is, sin(45deg), sin(0.125turn), and sin(3.14159 / 4) all represent the same value, approximately 0.707.