How to set the css of div to realize that background-img is placed at the bottom

my page is a div set and a div, wants to achieve the following effect:

is that the background only acts on the annular area and does not cover the div2.

clipboard.png

Baidu listed below, saying that it wants to set up zMui index, but the setting still has no effect. Xiaobai, ask for advice. Thank you.

<body>

    <!-- div1 --> 
    <div style="z-index: -100">

        <!-- div2 -->
        <div class="col-md-10 col-md-offset-1" style="margin: 20px 100px 20px 100px;box-shadow: 0px 0px 20px;z-index: 999">   Content  </div>


    </div>
</body>
Css
Mar.13,2021

Thank @ enhancer for his answer in the comments section. Setting the background color of div2 will not be rendered by the background color of div1.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3f95e-2c48e.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3f95e-2c48e.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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