Exclude height of existing div when setting viewport height for another div

Question

I'm working on a page that has a header nav, then two rows of banner images, then a couple more divs below the banners.

What I'd like to achieve is to have the nav div be a set height (90px) and then have the two rows of banners evenly split the remaining viewport height of the user's browser. Then, have the two divs below the banners also be fixed pixel heights.

Here's a snippet of my stripped down code:

html, body {
  margin: 0;
  padding: 0;
}

.nav {
  background: red;
  height: 90px;
  display: flex;
  justify-content: center;
  align-items: center;
}

.banners-row-1 {
  background: green;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 50vh;
}

.banners-row-2 {
  background: orange;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 50vh;
}

.mailing-list {
  height: 115px;
  background: pink;
  display: flex;
  justify-content: center;
  align-items: center;
}

.footer {
  height: 117px;
  background: lightblue;
  display: flex;
  justify-content: center;
  align-items: center;
}

<div class="nav">
  This is the nav
</div>
<div class="banners-row-1">
  Banners Row 1
</div>
<div class="banners-row-2">
  Banners Row 2
</div>
<div class="mailing-list">
  Mailing List
</div>
<div class="footer">
  Footer
</div>

As you can see, the two banner rows are set to 50vh, which is close to what I want - but, is there a way to somehow incorporate the 90px nav div when the banner divs calculate the viewport height?

Essentially, what I'm after is something along the lines of 50% of 'viewport height minus 90px'...?

Thanks

Answer 1

Wrap your nav and banners to wrapper and use following flex properties:

html, body {
  margin: 0;
  padding: 0;
}

.nav {
  background: red;
  height: 90px;
  display: flex;
  justify-content: center;
  align-items: center;
}
.wrap {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

.ban {
  flex: 1;
}
.banners-row-1 {
  background: green;
  display: flex;
  justify-content: center;
  align-items: center;
}

.banners-row-2 {
  background: orange;
  display: flex;
  justify-content: center;
  align-items: center;
}

.mailing-list {
  height: 115px;
  background: pink;
  display: flex;
  justify-content: center;
  align-items: center;
}

.footer {
  height: 117px;
  background: lightblue;
  display: flex;
  justify-content: center;
  align-items: center;
}

<div class="wrap">
  <div class="nav">
    This is the nav
  </div>
  <div class=" ban banners-row-1">
    Banners Row 1
  </div>
  <div class="ban banners-row-2">
    Banners Row 2
  </div>
</div>
<div class="mailing-list">
  Mailing List
</div>
<div class="footer">
  Footer
</div>

It works, because space in .wrap is splitted like: .nav has fixed 90px .bans have equal left space (100vh - 90px) / 2