在CSS中，您可以使用z-index屬性來(lái)控制盒子的層次關(guān)系。z-index屬性指定了元素在Z軸上的位置，即元素的堆疊順序，通過(guò)調(diào)整z-index的值，您可以控制盒子是否在***上層。
以下是一些示例代碼，展示如何使用z-index將盒子放在***上層：
示例1：使用z-index將盒子放在***上層
<!DOCTYPE html>
<html>
<head>
<style>
.box {
position: relative;
z-index: 999;
width: 200px;
height: 200px;
background-color: #f00;
}
</style>
</head>
<body>
<div class="box"></div>
<div style="position: relative; z-index: 1; background-color: #0f0; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 2; background-color: #00f; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 3; background-color: #ff0; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 4; background-color: #f0f; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 5; background-color: #0ff; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 6; background-color: #666; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 7; background-color: #333; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 8; background-color: #999; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 9; background-color: #666; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 10; background-color: #333; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 11; background-color: #999; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 12; background-color: #666; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 13; background-color: #333; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 14; background-color: #999; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 15; background-color: #666; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 16; background-color: #333; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 17; background-color: #999; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 18; background-color: #666; width: 200px; height: 200px;"></div>
<div style="position: relative; z-index: 19; background-color: #333; width: 2
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