Have div take up 1/6th of remaining parent div height - css

Question

I am attempting to make a simple calendar using css.
I have a parent div that will contain the calendar, and I have a div within that that contains the header with "Monday", "Tuesday", etc and is of fixed height. I now want to add divs that represent the rows of the calendar and split the remaining space into six even rows. However, I can't figure out how to divide the REMAINING space into 6 parts. Everything I try makes the div 1/6th of the parent div.
Any tips would be appreciated.
HTML:
<div id="parent>
<div id="header">
ST
</div>
<div class="row">
hi
</div>
</div>
CSS:
.row{
width:100%;
height: 16.66%;
background-color:red;
}

Answer 1

When you want to distribute remaining space left by a flexible element, flexbox is the answer.
html, body, #parent {
margin: 0;
height: 100%;
}
#parent {
display: flex;
flex-direction: column;
}
#header {
background-color: green;
}
.row {
width: 100%;
flex: 1; /* Distribute remaining space equally among the rows */
background-color: red;
}
.row:nth-child(odd) {
background-color: blue;
}
<div id="parent">
<div id="header">Header</div>
<div class="row"></div>
<div class="row"></div>
<div class="row"></div>
<div class="row"></div>
<div class="row"></div>
<div class="row"></div>
</div>

Answer 2

There are several ways to do that, and to pick one I need to know more how it should be used.
This sample simply use CSS calc() and subtract 1/6 of the header from 1/6 of the parent.
html, body {
margin: 0;
}
#parent {
height: 100vh;
}
#header {
height: 60px;
background-color:green;
}
.row{
height: calc(16.66% - 10px);
background-color:red;
}
.row:nth-child(odd){
background-color:blue;
}
<div id="parent">
<div id="header">
Header
</div>
<div class="row">
</div>
<div class="row">
</div>
<div class="row">
</div>
<div class="row">
</div>
<div class="row">
</div>
<div class="row">
</div>
</div>