How create a complex Bootstrap 4 layout - layout

Question

I just need put the box 7 below the box 6! But I can't...
All the code is below, to test in your machine please Include Bootstrap 4 from a CDN: https://www.w3schools.com/bootstrap4/bootstrap_get_started.asp
Ps: that is the desktop version, I don't need think about this layout in mobile version now.
Thank You!
.row {
background-color: yellow;
}
.row .row>div {
border:solid 1px black;
min-height:200px;
}
#box5 {
height: 400px;
background-color: lightgray;
}
#box6 {
height: 200px;
}
#box7 {
height: 200px;
}
#box8 {
height: 600px;
background-color: lightgray;
}
<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">
<!-- jQuery library -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<!-- Popper JS -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"></script>
<!-- Latest compiled JavaScript -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>
<div class="container">
<div class="row">
<div class="col-12">
<div class="row">
<div class="col-3">box 1</div>
<div class="col-9">box 2</div>
</div>
</div>
<div class="col-9">
<div class="row">
<div class="col-4">box 3</div>
<div class="col-8">box 4</div>
</div>
<div class="row">
<div class="col-4" id="box5">box 5</div>
<div class="col-8" id="box6">box 6</div>
<div class="col-8" id="box7">box 7</div>
</div>
</div>
<div class="col-3">
<div class="row">
<div class="col-12" id="box8">box 8</div>
</div>
</div>
</div>
</div>

Answer 1

#box5.col-4 and #box6.col-8 Both elements have fully occupied a row so that #box7 pushed out below #box5.
Use another div.row for #box6 and #box7 inside div.col-8.
.row {
background-color: yellow;
}
.row .row>div {
border: solid 1px black;
min-height: 200px;
}
#box5 {
height: 400px;
background-color: lightgray;
}
#box6 {
height: 200px;
}
#box7 {
height: 200px;
}
#box8 {
height: 600px;
background-color: lightgray;
}
<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">
<!-- jQuery library -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<!-- Popper JS -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"></script>
<!-- Latest compiled JavaScript -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>
<div class="container">
<div class="row">
<div class="col-12">
<div class="row">
<div class="col-3">box 1</div>
<div class="col-9">box 2</div>
</div>
</div>
<div class="col-9">
<div class="row">
<div class="col-4">box 3</div>
<div class="col-8">box 4</div>
</div>
<div class="row">
<div class="col-4" id="box5">box 5</div>
<div class="col-8">
<div class="row">
<div class="col-12" id="box6">box 6</div>
<div class="col-12" id="box7">box 7</div>
</div>
</div>
</div>
</div>
<div class="col-3">
<div class="row">
<div class="col-12" id="box8">box 8</div>
</div>
</div>
</div>
</div>

Answer 2

Here a simple solution to create that layout dynamicly with PHP.
You can use the same logic with another web language if you prefer.
<style>
.row {
border: solid 1px black;
min-height: 200px;
}
#box2 {
background-color: lightblue;
}
#box5 {
height: 400px;
background-color: lightgray;
}
#box6 {
height: 200px;
}
#box7 {
height: 200px;
}
#box8 {
height: 600px;
background-color: lightgray;
}
.container {
background-color: lightgreen;
}
#footer {
background-color: orange;
}
</style>
<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">
<!-- jQuery library -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<!-- Popper JS -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"></script>
<!-- Latest compiled JavaScript -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>
<?php
$total = 6; //from 1 to 6
?>
<?php for ($i=1; $i <= $total; $i++) :
if ($i==1) :
?>
<div class="container">
<div class="row">
<div class="col-12">
<div class="row">
<div class="col-3">box 1</div>
<div id="box2" class="col-9">box 2</div>
</div>
</div>
<?php
endif;
if ($i==2) :
?>
<div class="col-9">
<div class="row">
<div class="col-4">box 3</div>
<?php
endif;
if ($i==3) :
?>
<div class="col-8">box 4</div>
</div>
<div class="row">
<div class="col-4" id="box5">box 5</div>
<?php
endif;
if ($i==4) :
?>
<div class="col-8">
<div class="row">
<div class="col-12" id="box6">box 6</div>
<?php
endif;
if ($i==5) :
?>
<div class="col-12" id="box7">box 7</div>
</div>
<?php
endif;
if ($i==6) :
?>
</div>
</div>
</div>
<div class="col-3">
<div class="row">
<div class="col-12" id="box8">box 8</div>
</div>
</div>
</div>
</div>
<?php
endif;
endfor;
if ($total == 1) { echo '</div></div></div></div>'; }
if ($total == 2) { echo '</div></div></div></div></div></div>'; }
if ($total == 3) { echo '</div></div></div></div></div></div>'; }
if ($total == 4) { echo '</div></div></div></div></div></div></div></div>'; }
if ($total == 5) { echo '</div></div></div></div></div></div></div>'; }
?>
<div class="container-fluid" id="footer">
<div class="row">
<div class="col-12">
</div>
</div>
</div>