W3School TIY Editor

<!DOCTYPE html>
<html>
<head>
<style> 
#example1 {
  background-color: lightblue;
  height: 100px;
  width: 200px;
  border-start-start-radius: 50px;
}

#example2 {
  background-color: lightblue;
  height: 100px;
  width: 200px;
  border-start-start-radius: 50px 20px;
}

#example3 {
  background-color: lightblue;
  height: 100px;
  width: 200px;
  border-start-start-radius: 50%;
  direction: rtl;
}

#example4 {
  background-color: lightblue;
  height: 100px;
  width: 200px;
  border-start-start-radius: 50%;
  writing-mode: vertical-rl;
}
</style>
</head>
<body>

<h1>border-start-start-radius 属性</h1>

<p>border-start-start-radius 属性定义元素块级起始边和行内起始边之间角的半径。</p>

<div id="example1">
  <p>border-start-start-radius: 50px;</p>
</div>
<br>

<div id="example2">
  <p>border-start-start-radius: 50px 20px;</p>
</div>
<br>

<div id="example3">
  <p>border-start-start-radius: 50% 和 direction: rtl</p>
</div>
<br>

<div id="example4">
  <p>border-start-start-radius: 50% 和 writing mode: vertical-rl;</p>
</div>

</body>
</html>