The Shapes of CSS
All of the below use only a single HTML element. Any kind of CSS goes, as long as it's supported in at least one browser.
Square
Rectangle
Circle
Oval
Triangle Up
Triangle Down
Triangle Left
Triangle Right
Triangle Top Left
Triangle Top Right
Triangle Bottom Left
Triangle Bottom Right
Curved Tail Arrow via Ando Razafimandimby
Trapezoid
Parallelogram
Star (6-points)
Star (5-points) via Kit MacAllister
Pentagon
Hexagon
Octagon
Heart via Nicolas Gallagher
Infinity via Nicolas Gallagher
Diamond Square via Joseph Silber
Diamond Shield via Joseph Silber
Diamond Narrow via Joseph Silber
Cut Diamond via Alexander Futekov
Egg
Pac-Man
Talk Bubble
12 Point Burst via Alan Johnson
8 Point Burst via Alan Johnson
Yin Yang via Alexander Futekov
Badge Ribbon via Catalin Rosu
Space Invader via Vlad Zinculescu
TV Screen
Chevron via Anthony Ticknor
Magnifying Glass
Facebook Icon via Nathan Swartz
Moon via Omid Rasouli
Flag via Zoe Rooney
Cone via Omid Rasouli
Cross via Kaya Basharan
Base via Josh Rodgers
引：https://css-tricks.com/examples/ShapesOfCSS/