How to make a clickable responsive square box with centered content? - html

Question

I have a set of columns each containing a square box that fills to the column width and maintains a square height ratio.
The entire box needs to be clickable, with the content inside that also centered within the box. I can't figure out a way of getting the inner <a> element to fill out the space inside the parent div and have its own content centered.
Here is an editable Fiddle
The entire square should be red, entirely clickable, and with a centered download button within.
I've reviewed a bunch of similar questions about making square boxes with CSS but didn't find anything about the inner elements filling out the box like this.
Thanks
.block {
width: 100%;
height: 0;
padding-bottom: 100%;
border: 2px solid #600;
}
.block a {
display: flex;
justify-content: center;
align-items: center;
background: #C00;
text-decoration: none;
}
.block span {
padding: 1em;
border: 2px solid #FFF;
text-align: center;
color: #FFF;
}
/* Demo only */
.row {
display: flex;
justify-content: space-between;
}
.column {
width: 20%;
}
<div class="row">
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
</div>

Answer 1

Setting the parent .block to position: relative allows us to set .block > a to position: absolute, with dimensions that fill its parent; I only added 3 css rules, they're commented so you know which ones:
.block {
position: relative; /* change #1 */
width: 100%;
height: 0;
padding-bottom: 100%;
border: 2px solid #600;
}
.block a {
position: absolute; /* change #2 */
left: 0; right: 0; top: 0; bottom: 0; /* change #3 */
display: flex;
justify-content: center;
align-items: center;
background: #C00;
text-decoration: none;
}
.block span {
padding: 1em;
border: 2px solid #FFF;
text-align: center;
color: #FFF;
}
/* Demo only */
.row {
display: flex;
justify-content: space-between;
}
.column {
width: 20%;
}
<div class="row">
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
<div class="column">
<div class="block">
<a href="#">
<span>Download</span>
</a>
</div>
</div>
</div>