css - Grid item 100% height of parent

Question

The red sidebar in this page needs to be 100% of the container height:

body {
  display: grid;
  min-height: 85vh;
  grid-template-columns: auto 10fr 4fr;
  grid-template-rows: minmax(1rem, max-content) 1fr minmax(1rem, max-content);
  grid-template-areas: "header header aside" "main main aside" "footer footer footer";
}

header {
  grid-area: header;
  background: pink;
}

footer {
  grid-area: footer;
  background: blue;
}

main {
  grid-area: main;
  background: green;
}

aside {
  grid-area: aside;
  background: red;
  height: 100px;
  overflow-y: scroll;
}

<header> header </header>
<main>main</main>
<aside>
  aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>
</aside>
<footer> footer </footer>

Answer 1

Use min-height: 100%;height:0; to avoid the height of the aside affecting the layout then force it to be 100% height at the same time (height of its track defined by the other content)

body {
  display: grid;
  min-height: 85vh;
  grid-template-columns: auto 10fr 4fr;
  grid-template-rows: 
    minmax(1rem, max-content) 1fr minmax(1rem, max-content);
  grid-template-areas: 
    "header header aside" 
    "main   main   aside" 
    "footer footer footer";
}

header {
  grid-area: header;
  background: pink;
}

footer {
  grid-area: footer;
  background: blue;
}

main {
  grid-area: main;
  background: green;
}

aside {
  grid-area: aside;
  background: red;
  min-height: 100%;
  height:0;
  overflow-y: scroll;
}

<header> header </header>
<main>main</main>
<aside>
  aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>aside<br>
</aside>
<footer> footer </footer>