#square { width: 100px; height: 100px; background: red; }
有兴趣的话，最好是自己试试以下！······
#rectangle { width: 200px; height: 100px; background: red; }
#circle { width: 100px; height: 100px; background: red; -moz-border-radius: 50px; -webkit-border-radius: 50px; border-radius: 50px; } /* Cleaner, but slightly less support: use "50%" as value */
#oval { width: 200px; height: 100px; background: red; -moz-border-radius: 100px / 50px; -webkit-border-radius: 100px / 50px; border-radius: 100px / 50px; } /* Cleaner, but slightly less support: use "50%" as value */
#triangle-up { width: 0; height: 0; border-left: 50px solid transparent; border-right: 50px solid transparent; border-bottom: 100px solid red; }
#triangle-down { width: 0; height: 0; border-left: 50px solid transparent; border-right: 50px solid transparent; border-top: 100px solid red; }
#triangle-left { width: 0; height: 0; border-top: 50px solid transparent; border-right: 100px solid red; border-bottom: 50px solid transparent; }
#triangle-right { width: 0; height: 0; border-top: 50px solid transparent; border-left: 100px solid red; border-bottom: 50px solid transparent; }
#triangle-topleft { width: 0; height: 0; border-top: 100px solid red; border-right: 100px solid transparent; }
#triangle-topright { width: 0; height: 0; border-top: 100px solid red; border-left: 100px solid transparent; }
#triangle-bottomleft { width: 0; height: 0; border-bottom: 100px solid red; border-right: 100px solid transparent; }
#triangle-bottomright { width: 0; height: 0; border-bottom: 100px solid red; border-left: 100px solid transparent; }
#curvedarrow { position: relative; width: 0; height: 0; border-top: 9px solid transparent; border-right: 9px solid red; -webkit-transform: rotate(10deg); -moz-transform: rotate(10deg); -ms-transform: rotate(10deg); -o-transform: rotate(10deg); } #curvedarrow:after { content: ""; position: absolute; border: 0 solid transparent; border-top: 3px solid red; border-radius: 20px 0 0 0; top: -12px; left: -9px; width: 12px; height: 12px; -webkit-transform: rotate(45deg); -moz-transform: rotate(45deg); -ms-transform: rotate(45deg); -o-transform: rotate(45deg); }
#trapezoid { border-bottom: 100px solid red; border-left: 50px solid transparent; border-right: 50px solid transparent; height: 0; width: 100px; }
#parallelogram { width: 150px; height: 100px; -webkit-transform: skew(20deg); -moz-transform: skew(20deg); -o-transform: skew(20deg); background: red; }
#trapezoid { border-bottom: 100px solid red; border-left: 50px solid transparent; border-right: 50px solid transparent; height: 0; width: 100px; }
#star-six { width: 0; height: 0; border-left: 50px solid transparent; border-right: 50px solid transparent; border-bottom: 100px solid red; position: relative; } #star-six:after { width: 0; height: 0; border-left: 50px solid transparent; border-right: 50px solid transparent; border-top: 100px solid red; position: absolute; content: ""; top: 30px; left: -50px; }
#star-five { margin: 50px 0; position: relative; display: block; color: red; width: 0px; height: 0px; border-right: 100px solid transparent; border-bottom: 70px solid red; border-left: 100px solid transparent; -moz-transform: rotate(35deg); -webkit-transform: rotate(35deg); -ms-transform: rotate(35deg); -o-transform: rotate(35deg); } #star-five:before { border-bottom: 80px solid red; border-left: 30px solid transparent; border-right: 30px solid transparent; position: absolute; height: 0; width: 0; top: -45px; left: -65px; display: block; content: ''; -webkit-transform: rotate(-35deg); -moz-transform: rotate(-35deg); -ms-transform: rotate(-35deg); -o-transform: rotate(-35deg); } #star-five:after { position: absolute; display: block; color: red; top: 3px; left: -105px; width: 0px; height: 0px; border-right: 100px solid transparent; border-bottom: 70px solid red; border-left: 100px solid transparent; -webkit-transform: rotate(-70deg); -moz-transform: rotate(-70deg); -ms-transform: rotate(-70deg); -o-transform: rotate(-70deg); content: ''; }
#pentagon { position: relative; width: 54px; border-width: 50px 18px 0; border-style: solid; border-color: red transparent; } #pentagon:before { content: ""; position: absolute; height: 0; width: 0; top: -85px; left: -18px; border-width: 0 45px 35px; border-style: solid; border-color: transparent transparent red; }
#hexagon { width: 100px; height: 55px; background: red; position: relative; } #hexagon:before { content: ""; position: absolute; top: -25px; left: 0; width: 0; height: 0; border-left: 50px solid transparent; border-right: 50px solid transparent; border-bottom: 25px solid red; } #hexagon:after { content: ""; position: absolute; bottom: -25px; left: 0; width: 0; height: 0; border-left: 50px solid transparent; border-right: 50px solid transparent; border-top: 25px solid red; }
#octagon { width: 100px; height: 100px; background: red; position: relative; } #octagon:before { content: ""; position: absolute; top: 0; left: 0; border-bottom: 29px solid red; border-left: 29px solid #eee; border-right: 29px solid #eee; width: 42px; height: 0; } #octagon:after { content: ""; position: absolute; bottom: 0; left: 0; border-top: 29px solid red; border-left: 29px solid #eee; border-right: 29px solid #eee; width: 42px; height: 0; }
#heart { position: relative; width: 100px; height: 90px; } #heart:before, #heart:after { position: absolute; content: ""; left: 50px; top: 0; width: 50px; height: 80px; background: red; -moz-border-radius: 50px 50px 0 0; border-radius: 50px 50px 0 0; -webkit-transform: rotate(-45deg); -moz-transform: rotate(-45deg); -ms-transform: rotate(-45deg); -o-transform: rotate(-45deg); transform: rotate(-45deg); -webkit-transform-origin: 0 100%; -moz-transform-origin: 0 100%; -ms-transform-origin: 0 100%; -o-transform-origin: 0 100%; transform-origin: 0 100%; } #heart:after { left: 0; -webkit-transform: rotate(45deg); -moz-transform: rotate(45deg); -ms-transform: rotate(45deg); -o-transform: rotate(45deg); transform: rotate(45deg); -webkit-transform-origin: 100% 100%; -moz-transform-origin: 100% 100%; -ms-transform-origin: 100% 100%; -o-transform-origin: 100% 100%; transform-origin :100% 100%; }
#infinity { position: relative; width: 212px; height: 100px; } #infinity:before, #infinity:after { content: ""; position: absolute; top: 0; left: 0; width: 60px; height: 60px; border: 20px solid red; -moz-border-radius: 50px 50px 0 50px; border-radius: 50px 50px 0 50px; -webkit-transform: rotate(-45deg); -moz-transform: rotate(-45deg); -ms-transform: rotate(-45deg); -o-transform: rotate(-45deg); transform: rotate(-45deg); } #infinity:after { left: auto; right: 0; -moz-border-radius: 50px 50px 50px 0; border-radius: 50px 50px 50px 0; -webkit-transform: rotate(45deg); -moz-transform: rotate(45deg); -ms-transform: rotate(45deg); -o-transform: rotate(45deg); transform: rotate(45deg); }
#diamond { width: 0; height: 0; border: 50px solid transparent; border-bottom-color: red; position: relative; top: -50px; } #diamond:after { content: ''; position: absolute; left: -50px; top: 50px; width: 0; height: 0; border: 50px solid transparent; border-top-color: red; }
#diamond-shield { width: 0; height: 0; border: 50px solid transparent; border-bottom: 20px solid red; position: relative; top: -50px; } #diamond-shield:after { content: ''; position: absolute; left: -50px; top: 20px; width: 0; height: 0; border: 50px solid transparent; border-top: 70px solid red; }
#diamond-narrow { width: 0; height: 0; border: 50px solid transparent; border-bottom: 70px solid red; position: relative; top: -50px; } #diamond-narrow:after { content: ''; position: absolute; left: -50px; top: 70px; width: 0; height: 0; border: 50px solid transparent; border-top: 70px solid red; }
#cut-diamond { border-style: solid; border-color: transparent transparent red transparent; border-width: 0 25px 25px 25px; height: 0; width: 50px; position: relative; margin: 20px 0 50px 0; } #cut-diamond:after { content: ""; position: absolute; top: 25px; left: -25px; width: 0; height: 0; border-style: solid; border-color: red transparent transparent transparent; border-width: 70px 50px 0 50px; }
#egg { display:block; width: 126px; height: 180px; background-color: red; -webkit-border-radius: 63px 63px 63px 63px / 108px 108px 72px 72px; border-radius: 50% 50% 50% 50% / 60% 60% 40% 40%; }
#pacman { width: 0px; height: 0px; border-right: 60px solid transparent; border-top: 60px solid red; border-left: 60px solid red; border-bottom: 60px solid red; border-top-left-radius: 60px; border-top-right-radius: 60px; border-bottom-left-radius: 60px; border-bottom-right-radius: 60px; }
#talkbubble { width: 120px; height: 80px; background: red; position: relative; -moz-border-radius: 10px; -webkit-border-radius: 10px; border-radius: 10px; } #talkbubble:before { content:""; position: absolute; right: 100%; top: 26px; width: 0; height: 0; border-top: 13px solid transparent; border-right: 26px solid red; border-bottom: 13px solid transparent; }
#burst-12 { background: red; width: 80px; height: 80px; position: relative; text-align: center; } #burst-12:before, #burst-12:after { content: ""; position: absolute; top: 0; left: 0; height: 80px; width: 80px; background: red; } #burst-12:before { -webkit-transform: rotate(30deg); -moz-transform: rotate(30deg); -ms-transform: rotate(30deg); -o-transform: rotate(30deg); } #burst-12:after { -webkit-transform: rotate(60deg); -moz-transform: rotate(60deg); -ms-transform: rotate(60deg); -o-transform: rotate(60deg); }
#burst-8 { background: red; width: 80px; height: 80px; position: relative; text-align: center; -webkit-transform: rotate(20deg); -moz-transform: rotate(20deg); -ms-transform: rotate(20deg); -o-transform: rotate(20eg); } #burst-8:before { content: ""; position: absolute; top: 0; left: 0; height: 80px; width: 80px; background: red; -webkit-transform: rotate(135deg); -moz-transform: rotate(135deg); -ms-transform: rotate(135deg); -o-transform: rotate(135deg); }
#yin-yang { width: 96px; height: 48px; background: #eee; border-color: red; border-style: solid; border-width: 2px 2px 50px 2px; border-radius: 100%; position: relative; } #yin-yang:before { content: ""; position: absolute; top: 50%; left: 0; background: #eee; border: 18px solid red; border-radius: 100%; width: 12px; height: 12px; } #yin-yang:after { content: ""; position: absolute; top: 50%; left: 50%; background: red; border: 18px solid #eee; border-radius:100%; width: 12px; height: 12px; }
#badge-ribbon { position: relative; background: red; height: 100px; width: 100px; -moz-border-radius: 50px; -webkit-border-radius: 50px; border-radius: 50px; } #badge-ribbon:before, #badge-ribbon:after { content: ''; position: absolute; border-bottom: 70px solid red; border-left: 40px solid transparent; border-right: 40px solid transparent; top: 70px; left: -10px; -webkit-transform: rotate(-140deg); -moz-transform: rotate(-140deg); -ms-transform: rotate(-140deg); -o-transform: rotate(-140deg); } #badge-ribbon:after { left: auto; right: -10px; -webkit-transform: rotate(140deg); -moz-transform: rotate(140deg); -ms-transform: rotate(140deg); -o-transform: rotate(140deg); }
来源：https://www.cnblogs.com/asqq/archive/2012/04/13/2438861.html