input {
  margin: 24px;
}

.modal {
  height: 100%;
  width: 80%;
  background: linear-gradient(red, blue);
  overflow-y: auto;
}

.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  display: flex;
}

.modal-content {
  height: 200vh;
  margin-top: 50vh;
}

.input-position {
  border: 2px solid red;
  pointer-events: none;
  position: fixed;
}

.page-content {
  height: 2000px;
  background: linear-gradient(green, purple);
}

body {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

*, *::after, *::before {
  box-sizing: inherit;
}