zIndex with position：relative：not working chrome and safari

Question

在这个例子中有一个svg，其位置为：绝对在一个表上（位置：相对）。我希望表格的第一行覆盖“html”字样。在firefox中，我可以通过将第一行声明为position：使用z-index的相对广告来实现此目的。我无法理解为什么这不适用于chrome和Safari。我如何在Chrome和Safari中同样获得相同的结果？

在Safari和Chrome中：

在Firefox中：

#codexpl th, #codexpl td{
    padding:0.8em;
    border: 1px solid;
}
#codexpl th{
    background-color:#6699FF;
    font-weight:bold;
}

#codexpl{
  position: relative;
}

#svg{
  position:  absolute;
  top: 0;
  left: 0;
  width: 55%;
  z-index: 1;
}

tr:first-child{
  position: relative;
  z-index: 2;
}

<table id="codexpl">

   <tr>
        <th>#</th>
        <th>Columna</th>
        <th>Relative</th>
        <th>Isso</th>
    </tr>

    <tr>
        <td>1</td>
        <td>This</td>
        <td>Column</td>
        <td>Is</td>
    </tr>
    <tr>
        <td>2</td>
        <td>Coloumn</td>
        <td>two</td>
        <td>this</td>
    </tr>
    <tr>
        <td>3</td>
        <td>is</td>
        <td>not equals</td>
        <td>a</td>
    </tr>
    <tr>
        <td>4</td>
        <td>the</td>
        <td>Column</td>
        <td>real</td>
    </tr>
    <tr>
        <td>5</td>
        <td>first</td>
        <td>One</td>
        <td>Coloumn</td>
    </tr>

</table>

<svg id="svg" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
  <title>HTML5 Logo</title>
  
  <polygon fill="#E44D26" points="107.644,470.877 74.633,100.62 437.367,100.62 404.321,470.819 255.778,512             "/>
  <polygon fill="#F16529" points="256,480.523 376.03,447.246 404.27,130.894 256,130.894             "/>
  <polygon fill="#EBEBEB" points="256,268.217 195.91,268.217 191.76,221.716 256,221.716 256,176.305 255.843,176.305 142.132,176.305 143.219,188.488 154.38,313.627 256,313.627"/>
  <polygon fill="#EBEBEB" points="256,386.153 255.801,386.206 205.227,372.55 201.994,336.333 177.419,336.333 156.409,336.333 162.771,407.634 255.791,433.457 256,433.399"/>
  <path d="M108.382,0h23.077v22.8h21.11V0h23.078v69.044H152.57v-23.12h-21.11v23.12h-23.077V0z"/>
  <path d="M205.994,22.896h-20.316V0h63.72v22.896h-20.325v46.148h-23.078V22.896z"/>
  <path d="M259.511,0h24.063l14.802,24.26L313.163,0h24.072v69.044h-22.982V34.822l-15.877,24.549h-0.397l-15.888-24.549v34.222h-22.58V0z"/>
  <path d="M348.72,0h23.084v46.222h32.453v22.822H348.72V0z"/>
  <polygon fill="#FFFFFF" points="255.843,268.217 255.843,313.627 311.761,313.627 306.49,372.521 255.843,386.191 255.843,433.435 348.937,407.634 349.62,399.962 360.291,280.411 361.399,268.217 349.162,268.217"/>
  <polygon fill="#FFFFFF" points="255.843,176.305 255.843,204.509 255.843,221.605 255.843,221.716 365.385,221.716 365.385,221.716 365.531,221.716 366.442,211.509 368.511,188.488 369.597,176.305"/>
<svg>

Answer 1

只需更改此

tr:first-child{
  position: relative;
  z-index: 2;
}

到这个

tr:first-child th{//be specific to th
  position: relative;
  z-index: 2;
}