* {
  padding: 0;
  margin: 0;
}

body {
  overflow: hidden;
}

.button-container {
  width: 100vw;
  height: 100vh;
  background-color: #ffffff;
  opacity: 100%;
}

#trigger-modal,
.popup-modal {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

#trigger-modal {
  padding: 20px;
  color: #ffffff;
  background-color: #0e79dd;
  border: none;
  border-radius: 5px;
  font-weight: 600;
}

.popup-modal {
  width: 30%;
  height: 15%;
  background-color: white;
  border: 1px solid black;
  border-radius: 10px;
  display: flex;
  justify-content: center;
  align-items: center;
  margin-top: 10%;
  opacity: 0;
}

#close-modal {
  padding: 20px;
  color: #ffffff;
  background-color: #0e79dd;
  border: none;
  border-radius: 5px;
  font-weight: 600;
}

/* SOLUTION */

/* 
  Disclaimer: duplicating selectors here isn't best practice.
  We separated it out here to make it extra clear what has changed. 
*/

.button-container {
  transition: background-color 0.5s ease-in, opacity 0.5s ease-in;
}

.button-container.show {
  background-color: #000000;
  opacity: 40%;
}

#trigger-modal:hover,
#close-modal:hover {
  cursor: pointer;
  box-shadow: 1px 1px 2px #000000;
}

/* 
  Keep this '.popup-modal' selector separate from the main 
  .popup-modal selector, for the reasons outlined above 
  .pop-up-modal.show
*/
.popup-modal {
  visibility: hidden;
  transition: margin-top 0.5s ease-out, opacity 0.5s ease-out,
    visibility 0.5s linear;
}

/* 
  The common properties between .popup-modal and .popup-modal.show 
  can easily be added by just adding this selector to the main 
  .popup-modal selector
*/
.popup-modal.show {
  width: 30%;
  height: 15%;
  background-color: white;
  border: 1px solid black;
  border-radius: 10px;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 90px;
}

/* 
  Keep this selector separate from the main '.popup-modal.show'
  selector.
*/
.popup-modal.show {
  opacity: 1;
  visibility: visible;
  margin-top: 0;
  transition: margin-top 0.5s ease-out, opacity 0.5s ease-out,
    visibility 0.5s linear;
}