Fully responsive items with CSS grid and auto-fit minmax - html

Question

The use of grid-template-columns: repeat(auto-fit, minmax(600px, 1fr)) makes it easy to build a responsive CSS grid. The container will be filled with as many elements fit into a row, without using a media query.
.container {
display: grid;
grid-gap: 5px;
grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
}
.item {
height: 100px;
background: #ccc;
}
<div class="container">
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
</div>
The problem is that the items are wider than the screen when the screen is smaller than the min-value specified in minmax(). You can fix this by adding a media query at 400px, but this only works when you know that there's no content around the container. And that's almost impossible when the container could be placed anywhere.
Is there a way or property to tell the items that they should never be wider than 100%?
Something like: Fill the container with as many 400px items as possible, but ensure that non of them gets wider than 100% of the width of the container.
CodePen Demo

Answer 1

You should change grid-template-columns to grid-template-columns: repeat(auto-fit, minmax(min-content, 400px)) because minmax works this way: it tries to apply max value and if fails it applies minimum. But in this you can get blank space in your grid to the right. Demo:
.container {
display: grid;
grid-gap: 5px;
grid-template-columns: repeat(auto-fit, minmax(min-content, 400px));
}
.item {
height: 100px;
background: #ccc;
}
<div class="container">
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
</div>

Answer 2

Fill the container with as many 400px items as possible, but ensure that non of them gets wider than 100% of the width of the container.
For that you can use the "max-content" property, in your example this would be:
.unresponsive {
grid-template-columns: repeat(auto-fit, minmax(400px, auto));
grid-auto-columns: max-content;
}