Expanding cells in CSS grid layout - css

Question

I have the following HTML/CSS
.main {
display: grid;
grid-template-columns: 2fr 1fr;
}
/* The following is not essential - for decoration purposes only */
.left {
background-color: green;
}
.right {
background-color: orange;
}
<div class="main">
<div class="left">Left</div>
<div class="right">Right</div>
</div>
Now, sometimes, and depending on the div with class main, sometimes I do not have the div with the class right (in other words, the html might look like this
.main {
display: grid;
grid-template-columns: 2fr 1fr;
}
/* The following is not essential - for decoration purposes only */
.left {
background-color: green;
}
.right {
background-color: orange;
}
<div class="main">
<div class="left">Left</div>
</div>
What I like to do is write the CSS code in a way that expands div.left to the full width of the container div.main if div.right does not exist. How can I do that?

Answer 1

You can rely on implicit grid creation:
.main {
display: grid;
grid-template-columns: 2fr;
grid-auto-columns:1fr; /* this will trigger when you add the "right" element */
grid-auto-flow:column;
margin:5px;
}
.left {
background-color: green;
}
.right {
background-color: orange;
}
<div class="main">
<div class="left">Left</div>
<div class="right">right</div>
</div>
<div class="main">
<div class="left">Left</div>
</div>
It does also work if you want to remove left:
.main {
display: grid;
grid-template-columns: 2fr;
grid-auto-columns:1fr; /* this will trigger when you add the "left" element */
grid-auto-flow:column;
margin:5px;
}
.left {
background-color: green;
grid-column-end:1; /* added this */
}
.right {
background-color: orange;
}
<div class="main">
<div class="left">Left</div>
<div class="right">right</div>
</div>
<div class="main">
<div class="right">right</div>
</div>

Answer 2

This is something better suited to flexbox but if your structure is as simplistic as you indicate the only-child can be used here.
.main {
display: grid;
grid-template-columns: 2fr 1fr;
margin-bottom: 1em;
}
/* The following is not essential - for decoration purposes only */
.left {
background-color: green;
height: 25vh;
}
.left:only-child {
grid-column: 1 / -1;
}
.right {
background-color: orange;
}
<div class="main">
<div class="left">Left</div>
<div class="right">Right</div>
</div>
<div class="main">
<div class="left">Left</div>
</div>