Set display: table
for parent div and display: table-cell
for children divs
HTML :
<div class="container-fluid">
<div class="row justify-content-center display-as-table">
<div class="col-4 hidden-md-down" id="yellow">
XXXX<br />
XXXX<br />
XXXX<br />
XXXX<br />
XXXX<br />
XXXX<br />vv
XXXX<br />
</div>
<div class="col-10 col-sm-10 col-md-10 col-lg-8 col-xl-8" id="red">
Form Goes Here
</div>
</div>
</div>
CSS:
#yellow {
height: 100%;
background: yellow;
width: 50%;
}
#red {background: red}
.container-fluid {bacgkround: #ccc}
/* this is the part make equal height */
.display-as-table {display: table; width: 100%;}
.display-as-table > div {display: table-cell; float: none;}