白褶的博客

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Bin</title>
</head>
<body>
  <div class="parent">
    <div class="child">
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    </div>
  </div>
</body>
</html>

margin-top -50%

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  width: 300px;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -150px;
  height: 100px;
  margin-top: -50px;
}

translate -50%

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
}

absolute margin auto

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  position: absolute;
  width: 300px;
  height: 200px;
  margin: auto;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
}

flex

.parent{
  height: 600px;
  border: 3px solid red;

  display: flex;
  justify-content: center;
  align-items: center;
}
.child{
  border: 3px solid green;
  width: 300px;
}