html,body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  font-family: sans-serif;
}
.header {
  width: 100%;
  padding: 5px;
  background: black;
  color: white;
}
.modal {
  width: 100%;
  height: 100%;
  position: fixed;
  top: 0; left: 0;
  background: rgba(0,0,0,0.9);
  display: none;
}
.modal.visible {
  display: block;
}
.modal .inner {
  padding: 10px;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate3d(-50%,-50%,0);
  background: white;
  border-radius: 4px;
}

h1 {
  margin-top: 0;
}
.form > div {
  margin-bottom: 10px;
}
label {
  width: 150px;
  display: inline-block;
}
input {
  width: 200px;
  font-size: 15px;
  border: 1px solid #888;
  font-family: sans-serif;
  padding: 5px;
}
textarea {
  width: 320px;
  height: 160px;
  padding: 5px;
  font-size: 15px;
  border: 1px solid #888;
  margin-top: 10px;
}

button {
  font-size: 15px;
}