Center Img Vertical

HTML

<div class="textportfolio">
  <h1>This is a title</h1>
  
  <p class="textbio-small">
  The Roosevelt dime is the current ten-cent piece of the United States.
  </p>
  
  <img class="portfolio-slides-img" src="https://i.imgur.com/iheO43X.png">
  
  </div>

CSS

.textportfolio {
    font-family: "Lora", serif;
    margin: 5%;
    background: #e9cca3;
    height: 100vh
}

img.portfolio-slides-img {
    margin-top: 15%;
    max-width: 40%;
    max-height: 40%;
    margin: 0 auto;
    display: block;
    position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
    }