CSS2----implement triangles and angular frames

<! DOCTYPE html>
Realization of the principle of the triangle: 1,div border generation is outward, 2, when the Div has adjacent border, the corner will be in a half of the triangle together. So when the width of this div is 0 and 0 o'clock, if it has four border words, it will form a square, each side is a isosceles triangle, at this time if any three sides of the two side of the look of the transparent color (transparent), the remaining side is a isosceles triangle.
With the Angle box realization principle: Uses two triangle's relative localization to produce the visual subtraction to form the non-closed angle number (">").
CSS2----implement triangles and angular frames