Parallel Position Sticky Columns

HTML

<div class="pagecontent">
<div class="topbar"></div>
<div class="topbar-offset"></div>
  <div class="threecol">
    <div class="col col25">
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
    </div>
    <div class="col col60">
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
      <div class="heightblock"></div>
    </div>
    <div class="col col15">
      <div class="heightblock"></div>
    </div>
  </div>
</div>

CSS

.pagecontent {
  background: #FFF;
  width: 100%;
  min-height: 140px;
  position: relative;
}

.topbar {
  width: 100%;
  height:40px;
  position: fixed;
  background: #FFF;
  z-index: 999;
  top: 0;
  left: 0;
}

.topbar-offset {
  width: 100%;
  height: 40px;
  position: relative;
}

.threecol {
  width: 100%;
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
}

.threecol .col {
  min-height: 12px;
}

.threecol .col25 {
  width: 22%;
}

.threecol .col60 {
  width: 58%;
  padding-left: 2%;
  padding-right: 2%;
  margin: 0 2%;
  border-left: 1px solid rgba(33,33,33,0.2);
  border-right: 1px solid rgba(33,33,33,0.2);
  position: sticky;
  top: 45px;
}

.threecol .col15 {
  width: 13%;
  position: sticky;
  top: 45px;
}

.heightblock {
  width: 100%;
  height: 80px;
  margin-bottom: 4px;
}

.heightblock:nth-of-type(odd) {
  background: green;
}

.heightblock:nth-of-type(even) {
  background: yellow;
}