HTML
<div class="parent">
<div class="section yellow" contenteditable>
Min: 100px / Max: 25%
</div>
<div class="section blue" contenteditable>
This element takes the second grid position (1fr), meaning
it takes up the rest of the remaining space.
</div>
</div>
CSS
.parent {
display: grid;
grid-template-columns: minmax(100px, 25%) 1fr;
}