body {
  margin: 0;
  padding: 0;
  width: fit-content;
  min-width: 100%;
}

body > header {
  font-family: Mark Pro Book,Helvetica,Arial,sans-serif;
  font-size: 12px;
  line-height: 1em;

  position: sticky;
  z-index: 999;
  top: 0;
  left: 0em;
  padding-left: 1em;
  max-width: calc(100vw - 2.5em);
  height: 12em;
  background-color: #fff;
  border-bottom: 1px solid #000;
}
body > header > div.hide {
  display: none;
}
body > header > div > div.spacer {
  height: 1em;
}
body > header > div#input-calibration > div > input#calibrate_units {
  max-width: 6em;
}
body > header > div#output-measurement > div > span#result {
  font-size: 2em;
  font-weight: bold;
}

body > section#ruler-container {
  background-color: #000;
  position: relative;
}
body > section#ruler-container > img {
/*
  max-width: 100%;
  max-height: calc(100% - 12em);
*/
  margin: 0.25em;
}
body > section#ruler-container > div.ruler {
  position: absolute;
  z-index: 998;
  background-color: #000;
}
body > section#ruler-container > div.ruler.x-axis {
  height: 2px;
  /* dynamic onmousedown: top, left */
  /* dynamic onmousemove: width */
}
body > section#ruler-container > div.ruler.y-axis {
  width: 2px;
  /* dynamic onmousedown: top, left */
  /* dynamic onmousemove: height */
}

body > section#ruler-container > article#usage {
  background-color: #fff;
  font-family: Mark Pro Book,Helvetica,Arial,sans-serif;
  font-size: 16px;
  padding: 1em;
  text-align: center;
}
body > section#ruler-container > article#usage > div {
  display: inline-block;
  margin: 0 auto;
  text-align: left;
}