input / button elements not shrinking in a flex container

When using input and button elements inside a flex container, the flex and/or flex-grow properties don't seem to do anything.

Code that demonstrates my issue.

button,
input {
  font-size: 1rem;
}

button {
  border: none;
  background-color: #333;
  color: #EEE;
}

input {
  border: 1px solid #AAA;
  padding-left: 0.5rem;
}

.inputrow {
  width: 30rem;
  display: flex;
  margin: 0 -.25rem;
}

.inputrow>* {
  margin: 0 .25rem;
  border-radius: 2px;
  height: 1.75rem;
  box-sizing: border-box;
}

.nickname {
  flex: 1;
}

.message {
  flex: 4;
}

.s-button {
  flex: 1;
}

<div class="inputrow">
  <input type="text" class="nickname" placeholder="Nickname">
  <input type="text" class="message" placeholder="Message">
  <button type="submit" class="s-button">Submit</button>
</div>

Code that shows what I'm expecting. (using DIVs instead of input and button).

.inputrow {
  width: 30rem;
  display: flex;
  flex-flow: row nowrap;
  margin: 0 -.25rem;
}

.inputrow>* {
  margin: 0 .25rem;
  height: 1.75rem;
}

.nickname {
  flex: 1;
  background-color: blue;
}

.message {
  flex: 4;
  background-color: red;
}

.s-button {
  flex: 1;
  background-color: green;
}

<div class="inputrow">
  <div class="nickname">Nickname</div>
  <div class="message">Message</div>
  <div class="s-button">Submit</div>
</div>

An input element, unlike a div, comes with a default width.

Here's a simple illustration of this setting:

The browser automatically gives the input a width.

input {
  border: 1px solid blue;
  display: inline;
}

div {
  border: 1px solid red;
  display: inline;
}

<form>
  <input>
  <br><br>
  <div></div>
</form>

Also, an initial setting on flex items is min-width: auto. This means that items cannot shrink below their width on the main axis.

Hence, input elements cannot shrink below their default width and may be forced to overflow the flex container.

You can override this behavior by setting your inputs to min-width: 0 (revised codepen)

Here's a full explanation: https://stackoverflow.com/q/36247140/3597276

In some cases, you may need to override input widths using width: 100% or width: 0.

I would like to extend @Michael Benjamin solution

> In some cases, you may need to override input widths using width: 100% or width: 0.

you can also do calc(100%)

I needed to wrap the input element with a styled element and than set the input width and min-width as below:

.field__input input {
    width: 0;
    min-width: 100%;
}

if the parent is a flexible container set with the usual flex: 1 (flex-grow: 1) and you want the input to shrink with the parent, this is what has worked for me:

width: 35px;
flex: 1 2 0px;

Give this as a class to the input, this will make it take the whole space when its available, but shrink to minimum size when resized.

Edit:

This works because it's a shorthand for flex: <flex-grow> <flex-shrink> <flex-basis> as explained here https://css-tricks.com/snippets/css/a-guide-to-flexbox/#flex

The '2' is assigned to flex-shrink which makes the element shrink. Sometimes you still need to add min-width: 0; as mentioned in other comments to remove the min-width defined by browsers (for small containers)

If you have an input element inside a flex box, you can defined the width: 0 and still can utilize flex: 1 or whatever value you need.

This is Christof Kälin's answer in the comments for another answer. Putting it here for visibility.

Here is the link from his answer with working copy: https://jsbin.com/zutahalawa/edit?html,css,output

Making this answer a community wiki so that I don't get unearned credit.

Use flex-basis: 0; for input or input container solves the problem.