<div class="overlay">
  <div class="popup">
    <h2>Do you like money?</h2>
    <p>Send us your credit card details to get free money.</p>
    <button>Sounds fishy.</button>
    <button>Yes, I love money!</button>
  </div>
</div>

* {
  box-sizing: border-box;
}

body, html {
  height: 100%;
  overflow: hidden;
}

* {
  box-sizing: border-box;
}

body, html {
  height: 100%;
  overflow: hidden;
}

.overlay { 
  height: 100%;
  width: 100%;
  background: rgba(0, 0, 0, 0.4);
  display: flex;
  justify-content: center;
  align-items: center;
}

.popup {
  border-radius: 8px;
  border: 1px solid grey;
  padding: 2rem;
  background-color: rgba(255, 255, 255, 1);
  min-width: 240px;
  max-width: 80%;
  box-shadow: 
    0 7px 8px -4px rgba(0,0, 0, 0.2),
    0 13px 19px 2px rgba(0, 0, 0, 0.14),
    0 5px 24px 4px rgba(0, 0, 0, 0.12);
}

button { 
  border-width: 0;
  border-radius: 4px;
  background-color: rgba(225, 225, 225, 1);
  padding: 1rem;
  color: rgba(95, 95, 95, 1);
  box-shadow: 
    0 1px 3px 0 rgba(0,0,0,.2), 
    0 1px 1px 0 rgba(0,0,0,.14), 
    0 2px 1px -1px rgba(0,0,0,.12);
  cursor: pointer;
  font-weight: 700;
  margin-top: 1rem;
  margin-right: 0.75rem;
}

button:hover {
  background-color: rgb(198,200,201);
}