The twisting bar is rendered using <hr> elements whose border and color follow a curve. The borders are solid and sized fraction of in hence the subtitle of this intro.
This calculation q=0>(p=E.cos(O+=22))(P=E.sin(O)) hits three birds. It computes and stores the length of both visible sides of the twisting bar in p and P and check and stores which one goes left by compairing q=0>=pP.
With this three values the border-right and border-left of the <hr> element can style properly, setting the width to according to the visible sides of the bar and setting the color by casting q like this (9-q)36 or (8+q)36. Combined with the subtitle of this intro, this gives the colors #288 and #324.
Hope this answers any questions you had about this effect.