style.css

/* Based on https://stackoverflow.com/questions/90178/make-a-div-fill-the-height-of-the-remaining-screen-space/16960823 */

html,
body {
  height: 99%;
  margin: 2px;
}

.box {
  display: flex;
  flex-flow: column;
  height: 100%;
}

.box .row {
  border: none;
}

.box .row.header {
  flex: 0 1 auto;
  /* The above is shorthand for:
  flex-grow: 0,
  flex-shrink: 1,
  flex-basis: auto
  */
}

.box .row.content {
  flex: 1 1 auto;
}

/* https://www.w3schools.com/css/css3_buttons.asp */
.button {
  background-color: #008CBA; /* Blue */
  border-style: solid;
  color: white;
  padding: 15px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  width: 30%;
}