HTML and CSS Reference
The format of an <angle> is expressed as a <number> followed immediately by an angle
unit. There are four types of angle units: degrees ( deg ), grads ( grad ), radians ( rad ), and
turns ( turn ). For example, a right angle could be declared as 90deg , 100grad , 1.571rad , or
0.25turn ; in each case, the values are translated into degrees in the range 0 through 360. This
is also true of negative values, which are allowed. The measure −90deg is the same as 270deg .