radius，就是半徑的意思。用這個屬性可以很容易做出圓角效果，當然，也可以做出圓形效果。原理很簡單，“正方形的內切圓的半徑等于正方形邊長的一半”。下面就做一個紅色的圓。<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>CSS3的border-radius屬性</title> <style> .circle { background-color:#f00; width: 600px; /* div的寬和高為600px即正方形的邊長為600px */ height: 600px; text-align: center; -moz-border-radius: 300px; /* 圓的半徑為邊長的一半，即300px */ -webkit-border-radius: 300px; border-radius: 300px; display: -moz-box; display: -webkit-box; display: box; -moz-box-orient: horizontal; -webkit-box-orient: horizontal; box-orient: horizontal; -moz-box-pack: center; -moz-box-align: center; -webkit-box-pack: center; -webkit-box-align: center; box-pack: center; box-align: center; font:normal 80px/100% Arial; text-shadow:1px 1px 1px #000; color:#fff; } </style> </head> <body> <div class="circle"> Hello,World! </div> </body> </html>接下來用這個屬性做一個奧運五環，與前面不同的是，圓環是有邊的厚度的，這里用的是相對單位em。
<!DOCTYPE html> <html> <head> <meta charset="UTF-8" /> <title>The Olympic Flag</title> <style type="text/css" media="screen"> body { margin:20px; background-color:#efefef; } ul.flag { list-style-type:none; position: relative; margin: 20px auto; } .flag li, .flag li:before, .flag li:after { -webkit-border-radius: 6em; -moz-border-radius: 6em; border-radius: 6em; position: absolute; } .flag li { width: 12em; height: 12em; left: 0; top: 0; font-size: 1em; } .flag li:after { display: block; content: ""; top: -0.1em; left: -0.1em; right: -0.1em; bottom: -0.1em; border: solid 1.4em black; } .flag .blue { z-index: 10; left: 0; top: 0; } .flag .yellow { z-index: 20; left: 6.8em; top: 5.7em; } .flag .black { z-index: 21; left: 13.6em; top: 0; } .flag .green { z-index: 20; left: 20.4em; top: 5.7em; } .flag .red { z-index: 10; left: 27.2em; top: 0px; } .flag .blue:after { border-color: blue; } .flag .yellow:after { border-color: yellow; } .flag .black:after { border-color: black; } .flag .green:after { border-color: green; } .flag .red:after { border-color: red; } /* 藍色壓住黃色 */ .flag .blue.alt { z-index: 24; } .flag .blue.alt, .flag .blue.alt:before, .flag .blue.alt:after { border-top-color: transparent; border-left-color: transparent; border-bottom-color: transparent; } /* 黃色壓住黑色 */ .flag .yellow.alt { z-index: 23; } .flag .yellow.alt, .flag .yellow.alt:before, .flag .yellow.alt:after { border-right-color: transparent; border-left-color: transparent; border-bottom-color: transparent; } /* 綠色壓住黑色 */ .flag .green.alt { z-index: 23; } .flag .green.alt, .flag .green.alt:before, .flag .green.alt:after { border-top-color: transparent; border-right-color: transparent; border-bottom-color: transparent; } /* 紅色壓住綠色 */ .flag .red.alt { z-index: 23; } .flag .red.alt, .flag .red.alt:before, .flag .red.alt:after { border-top-color: transparent; border-right-color: transparent; border-left-color: transparent; } </style> </head> <body> <ul class="flag"> <li class="blue"></li> <li class="blue alt"></li> <li class="yellow"></li> <li class="yellow alt"></li> <li class="black"></li> <li class="green"></li> <li class="green alt"></li> <li class="red"></li> <li class="red alt"></li> </ul> </body> </html>
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