Wrapping error with flexbox

Question

I have two DIVs, one of them with fixed height, and the other should cover the rest of the page. Both are placed in a wrapper DIV. Now, if I the second DIV's content overflows, I want the DIV to scroll (not the page). My current problem is that the second div doesn't align vertically with the first. I don't understand what mistake I've done here, maybe you can spotit:

#wrapper, body, html{
  height: 100vh;
}
#topbar {
  width: 100%;
  height: 2em;
  border-bottom: $color 0.15em solid;
  display: flex;
  padding-left: 1em;
  div {
    line-height: 2em;
    padding: 0 0.5em;
    cursor: default;
    transition: background 0.3s;
    &:hover {
      background: $accent;
    }
  }
}
#wrapper {
  display: flex;
  flex-wrap: wrap;
  flex-direction: column;
}
#main {
  display: flex;
  flex-grow: 1;
  overflow: auto;
  .main-column {
    border-left: $color 0.15em solid;
    flex-grow: 1;
  }
}

http://codepen.io/Chrisstar/pen/LRrOKP

Answer 1

Not sure if I got your question/request correct but is this what you mean;

$dark: #292929;
$color: #7CB342;
$accent: #5F8339;
body {
  background: $dark;
  font-family: 'Open Sans', Helvetica, Arial, sans-serif;
  height: 100%;
  font-size: 16px;
  color: white;
}
#wrapper, body, html{
  height: 100vh;
}
#topbar {
  width: 100%;
  min-height: 2em;
  max-height: 2em;
  border-bottom: $color 0.15em solid;
  display: flex;
  padding-left: 1em;
  position: fixed;
  .bar-item {
    line-height: 2em;
    padding: 0 0.5em;
    cursor: default;
    transition: background 0.3s;
    &:hover {
      background: $accent;
    }
  }
}
#wrapper {
  display: flex;
  flex-wrap: wrap;
  flex-flow: column;
}
#main {
  margin-top: 2em;
  display: flex;
  flex-grow: 1;
  overflow: auto;
  position: relative;
  .main-column {
    max-height: 100%;
    border-left: $color 0.15em solid;
    flex: 1;
  }
}
*, *::before, *::after {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}

<div id="wrapper">
  <div id="topbar">
    <div class="bar-item">One</div>
    <div class="bar-item">Two</div>
  </div>
  <div id="main">
    <div class="main-column">
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
      e<br />
    </div>
    <div class="main-column">
w
    </div>
    <div class="main-column">
w
    </div>
  </div>
</div>

Answer 2

you may use flex-flow instead flex-direction and apply it to .main too.:

body {
  background: #292929;
  font-family: 'Open Sans', Helvetica, Arial, sans-serif;
  height: 100%;
  font-size: 16px;
  color: white;
  margin: 0;
}

#wrapper, body, html {
  height: 100vh;
}

#topbar {
  width: 100%;
  height: 2em;
  border-bottom: #7CB342 0.15em solid;
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  padding-left: 1em;
}
#topbar div {
  line-height: 2em;
  padding: 0 0.5em;
  cursor: default;
  -webkit-transition: background 0.3s;
  transition: background 0.3s;
}
#topbar div:hover {
  background: #5F8339;
}

#wrapper {
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-flex-wrap: wrap;
      -ms-flex-wrap: wrap;
          flex-wrap: wrap;
  -webkit-flex-flow: column;
      -ms-flex-flow: column;
          flex-flow: column;
  /* update */
}

#main {
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-flex-flow: column;
      -ms-flex-flow: column;
          flex-flow: column;
  /* update */
  -webkit-box-flex: 1;
  -webkit-flex-grow: 1;
      -ms-flex-positive: 1;
          flex-grow: 1;
  overflow: auto;
}
#main .main-column {
  border-left: #7CB342 0.15em solid;
  -webkit-box-flex: 1;  
  -webkit-flex-grow: 1;
      -ms-flex-positive: 1;
          flex-grow: 1;
}

*, *::before, *::after {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}

<div id="wrapper">
  <div id="topbar">
    <div>One</div>
    <div>Two</div>
  </div>
  <div id="main">
    <div class="main-column">
      e<br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br /> e
      <br />
    </div>
    <div class="main-column">
      w
    </div>
    <div class="main-column">
      w
    </div>
  </div>
</div>

http://codepen.io/gc-nomade/pen/jrXpzL