Skew X (anticlockwise).
transform: skew(30deg);

Skew X (clockwise).
transform: skew(-30deg);

Skew X (anticlockwise in radians).
transform: skew(0.5rad);

Skew X and Y (anticlockwise).
transform: skew(15deg, 15deg);

Skew X only (anticlockwise).
transform: skewX(15deg);

Skew Y only (anticlockwise).
transform: skewY(15deg);