html图片设置fixed消失,为什么fixed后，DIV7消失了，怎么显示出来？

HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"

"http://www.w3.org/TR/html4/loose.dtd">

#div1{

width: 200px;

height: 200px;

background-color: #4061f5;

}

#div2{

width: 300px;

height: 300px;

background-color: #eff57b;

}

#div3{

width: 200px;

height:300px;

background-color: #f52e16;

}

#div4{

width: 100px;

height: 100px;

background-color: #70f5b1;

}

#div5{

width: 100px;

height: 100px;

background-color: #f595a6;

}

#div6{

width: 100px;

height: 100px;

background-color: #c500f5;

}

#div7{

border: 1px solid saddlebrown;

width: 50px;

height: 50px;

background-color: #f5783a;

position: fixed;

}

div{

margin:0;

padding: 0;

}

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