<a href="#example1" class="btn">Open modal</a>

<div class="lightbox" id="example1">
   <figure class="lightbox__body">
      <a href="#" class="lightbox__close-btn"></a>
      <figcaption class="lightbox__content">
         <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec felis enim, placerat id eleifend eu, semper vel sem. Sed interdum commodo enim venenatis pulvinar.</p>
      </figcaption>
   </figure>
</div>

body {
   padding: 40px;
   background: #efefef;
}

.btn {
   background: #24abf2;
   color: #fff;
   padding: 15px;
   font-weight: 700;
   display: inline-block;
   font-size: 14px;
   text-decoration: none;
   position: absolute;
   top: 50%;
   left: 50%;
   transform: translate(-50%, -50%);
}

.lightbox {
    display: none;
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
}

.lightbox:target {
    display: flex;
    justify-content: center;
    align-items: center;
}

.lightbox__body {
    width: 400px;
    position: relative;
}

.lightbox__content {
    background: #fff;
    padding: 40px;
    border-radius: 2px;
    position: relative;
    
    p {
        margin: 0;
        font-size: 14px;
        line-height: 1.6em;
        color: #444;
    }
}

.lightbox__close-btn::after {
    content: "Close";
    display: inline-block;
    position: absolute;
    right: -15px;
    top: -15px;
    z-index: 3;
    width: auto;
    height: 30px;
    cursor: pointer;
    background: #000;
    font-weight: 700;
    font-size: 11px;
    padding: 0 15px;
    line-height: 30px;
    color: #fff;
}

.lightbox__close-btn::before {
    content: "";
    display: block;
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background-color: rgba(0, 0, 0, 0.7);
}