<body>

  <div class="some-text">
    <p>
      This is a <span class="pure">pure</span> CSS Popup.
    </p>
    <a class="button" href="#popup">I am a Popup<a />
  </div>

  <div class="popup" id="popup">
    <div class="popup__content">
        <h2 class="heading-secondary">Start booking now</h2>
        <h3 class="heading-tertiary">Important &ndash; Please read these terms before booking</h3>
        <p class="popup__text">
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        </p>
        <a href="#" class="button">Close Popup</a>
    </div>
  </div>

</body>
// 3rd Party Imports
@import url('https://fonts.googleapis.com/css?family=Poppins:200,300,400,500,600,700,800,900&display=swap');

// Variables

// Mixins
@mixin absCenter {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

// SCSS
* {
  margin: 0;
  padding: 0;
  font-family: 'Poppins';
  box-sizing: border-box;
}

html {
  height: 100vh;
}

body {
  min-height: 100vh;
}

.some-text {
  @include absCenter;
  max-width: 800px;
  text-align: center;
  font-weight: 500;
  font-size: 24px;
}

.pure {
  color: #e75480;
  text-decoration: underline;
  font-weight: 600;
}

.button {
  background-color: #4CAF50; /* Green */
  border: none;
  color: white;
  padding: 15px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  border-radius: 100px;
  margin-top: 25px;
}

.popup {
  height: 100vh;
  width: 100%;
  position: fixed;
  top: 0;
  left: 0;
  background-color: rgba(black, .8);
  backdrop-filter: blur(10px);
  z-index: 9999;
  opacity: 0;
  visibility: hidden;
  transition: all .3s;

  // The url changes when the anchor is triggered and CSS can watch that
  &:target {
    opacity: 1;
    visibility: visible;
  }
  
  &__content {
    @include absCenter; // Our mixin to center horizontally and vertically

    width: 75%;
    padding: 20px;
    background-color: white;
    box-shadow: 0 2rem 4rem rgba(black, .2);
    border-radius: 10px;
    overflow: hidden; // This will keep the images sharp corners from protruding past the border-radius

  }

  &__text {
    font-size: 1.4rem;
    margin-bottom: 4rem;
  }
}
View Compiled 
// console.log(`Running...`)
View Compiled

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.