1 <!DOCTYPE html> 2 <html> 3 <head> 4 <meta charset="UTF-8"> 5 <title></title> 6 <style> 7 8 .test1{ 9 width: 100px; 10 height: 100px; 11 border: 1px solid green; 12 background: green; 13 position: absolute; 14 z-index: auto; 15 } 16 17 .test2{ 18 width: 100px; 19 height: 100px; 20 border: 1px solid black; 21 background: black; 22 position: relative; 23 left: 20px; 24 top: -20px; 25 z-index: -1; 26 } 27 </style> 28 </head> 29 <body> 30 <div class="test1"> 31 <div class="test2"></div> 32 33 </div> 34 35 </body> 36 </html>
父元素不设置z-index 的值时，默认是auto。此时在设置子元素的值为负数
