https://arts-factory.net/position/
HTML
<div class=”box”>
<p>テキストテキスト</p>
<img src=xxx.jpg width=”600″ height=”400″ alt=”xxxx” >
</div>
CSS
.box{
position: relative;
}
.box p{
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
-webkit-transform: translate(-50%, -50%);
-ms-transform: translate(-50%, -50%);
}