html - input / button elements not shrinking in a flex container

Question

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>

Answer 1

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>