vertical divider between two columns in bootstrap

Well here's another option which I've been using for some time now. It works great for me since I mostly need it do visually separate 2 cols. And it's also responsive. Which means that if I have columns next to each other in medium and large screen sizes, then I would use the class col-md-border, which would hide the separator on smaller screen sizes.

css:

@media (min-width: 992px) {
    .col-md-border:not(:last-child) {
        border-right: 1px solid #d7d7d7;
    }
    .col-md-border + .col-md-border {
        border-left: 1px solid #d7d7d7;
        margin-left: -1px;
    }
}

In scss you can generate all needed classes probably from this:

scss:

@media(min-width: $screen-md-min) {
    .col-md-border {
        &:not(:last-child) {
            border-right: 1px solid #d7d7d7;
        }

        & + .col-md-border {
            border-left: 1px solid #d7d7d7;
            margin-left: -1px;
        }
    }
}

HTML:

<div class="row">
    <div class="col-md-6 col-md-border"></div>
    <div class="col-md-6 col-md-border"></div>
</div>  

How it works:

The cols must be inside an element where there are no other cols otherwise the selectors might not work as expected.

.col-md-border:not(:last-child) matches all but the last element before .row close and adds right border to it.

.col-md-border + .col-md-border matches the second div with the same class if these two are next to each other and adds left border and -1px negative margin. Negative margin is why it doesn't matter anymore which column has greater height and the separator will be 1px the same height as the highest column.

It does also have some problems...

1. When you try to be clever/lazy and use col-XX-X class together with hidden-XX/visible-XX classes inside the same row element.
2. When you have a lot of columns and need a pixel perfect thing. Since it moves n-1 column 1px to the left.

... But on the other hand it's responsive, works great for simple html and it's easy to create these classes for all bootstrap screen sizes.

.row.vertical-divider {
  overflow: hidden;
}
.row.vertical-divider > div[class^="col-"] {
  text-align: center;
  padding-bottom: 100px;
  margin-bottom: -100px;
  border-left: 3px solid #F2F7F9;
  border-right: 3px solid #F2F7F9;
}
.row.vertical-divider div[class^="col-"]:first-child {
  border-left: none;
}
.row.vertical-divider div[class^="col-"]:last-child {
  border-right: none;
}

<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" rel="stylesheet" />
<div class="row vertical-divider" style="margin-top: 30px">
  <div class="col-xs-6">Hi there</div>
  <div class="col-xs-6">Hi world<br/>hi world</div>
</div>

In Bootstrap 4 there is the utility class border-right which you can use.

So for example you can do:

<div class="row">
  <div class="col-6 border-right"></div>
  <div class="col-6"></div>
</div>

If your code looks like this:

<div class="row">
  <div class="span6">
  </div>
  <div class="span6">
  </div>
</div>

Then I'd assume you're using additional DIVS within the "span6" DIVS for holding/styling your content? So...

<div class="row">
  <div class="span6">
    <div class="mycontent-left">
    </div>
  </div>
  <div class="span6">
    <div class="mycontent-right">
    </div>
  </div>
</div>

So you could simply add some CSS to the "mycontent-left" class to create your divider.

.mycontent-left {
  border-right: 1px dashed #333;
}