#prompt-overlay {
  /* display: none; set directly in html
     for easier js manipulation */
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color:rgba(0,0,0,0.5);
}

#prompt-wrapper {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;

  margin: auto;
  width: 70%;
  height: auto;
  min-height: 500px;
  max-height: 70%;

  padding: 30px;
  background-color: #fff;
  box-shadow: 0 0 30px #000;
}

#prompt {
  overflow: scroll;
}

#prompt input[type="text"] {
  margin: 10px 30px 0 5px;
  width: 80px;
}

#prompt a[class="button"] {
  display: inline-block;
  margin: 10px;
}

#prompt-close-button {
  float: right;
  text-decoration: none;
  color: #000;
  font-size: 1.3em;
  font-weight: bold;
}

#prompt-overlay {
  /* display: none; set directly in html
     for easier js manipulation */
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color:rgba(0,0,0,0.65);
}

#prompt-wrapper {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;

  margin: auto;
  width: 70%;
  height: auto;
  min-height: 500px;
  max-height: 70%;

  padding: 30px;
  background-color: #fff;
  box-shadow: 0 0 30px #000;
}

#prompt {
  overflow: scroll;
}

#prompt input[type="text"] {
  margin: 10px 30px 0 5px;
  width: 80px;
}

#prompt a[class="button"] {
  display: inline-block;
  margin: 10px;
}

#prompt-close-button {
  float: right;
  text-decoration: none;
  color: #000;
  font-size: 1.3em;
  font-weight: bold;
}

Make the prompt background darker
Make the prompt background darker
