.menu {
  overflow-x: hidden;
  overflow-y: scroll;
  float: left;
  height: 100vh;
  width: 250px;
  background: $off-gray;
  border-right: 1px solid $off-gray;
  @include osx-scrollbar;
  @include osx-scrollbar-vt;

  > .main-heading {
    margin: 0;
    padding: 10px 20px;
    color: $white;
    text-align: center;
    background: $black;
  }

  > .logo-container {
    display: block;
    padding: 20px 0;
    text-align: center;
  }

  > .logo-container > img {
    width: 150px;
    height: 150px;
  }

  > section > .heading {
    margin: 0; // remove vertical rhythm 
    padding: 15px 20px;
  }

  > section > .heading.-bordered {
    border-top: 1px solid $off-gray;
  }

  > section > a {
    display: block;
    padding: 10px 20px;
    color: $black;
    background: $white;
    border-bottom: 1px solid $off-gray;
    transition: 0.12s all;

    &, &:hover {
      text-decoration: none;
    }

    &:hover,
    &.-active {
      background: $black;
      color: $white;
    }
  }
}

.menu {
  position: fixed;
  overflow-x: hidden;
  overflow-y: scroll;
  float: left;
  height: 100vh;
  width: 250px;
  background: $off-gray;
  border-right: 1px solid $off-gray;
  @include osx-scrollbar;
  @include osx-scrollbar-vt;

  > .main-heading {
    margin: 0;
    padding: 10px 20px;
    color: $white;
    text-align: center;
    background: $black;
  }

  > .logo-container {
    display: block;
    padding: 20px 0;
    text-align: center;
  }

  > .logo-container > img {
    width: 150px;
    height: 150px;
  }

  > section > .heading {
    margin: 0; // remove vertical rhythm 
    padding: 15px 20px;
  }

  > section > .heading.-bordered {
    border-top: 1px solid $off-gray;
  }

  > section > a {
    display: block;
    padding: 10px 20px;
    color: $black;
    background: $white;
    border-bottom: 1px solid $off-gray;
    transition: 0.12s all;

    &, &:hover {
      text-decoration: none;
    }

    &:hover,
    &.-active {
      background: $black;
      color: $white;
    }
  }
}

Set menu to fixed pos
Set menu to fixed pos