Why does the width of a form input shorten when it's inside a container with display: flex?

Question

The design I'm trying to code:

I attempted to code this design of form input, but I encountered a problem when I used display: flex. The width of the input shortens instead of expanding as I expected.

The result of my code:

Here are the results of what I did, the width of my form input is already set to 100%. I have it in display: flex because I need the dropdown, input, and search button to stick together. Anyway, here's my code. Please let me know if anything is incorrect.

.search-button {
  display: flex;
  justify-content: left;
  margin-left: .4em;
  margin-bottom: 1em;
}

.div-1-s1 {
  font-family: 'Plus Jakarta Sans', sans-serif;
  font-size: 0.875rem;
  font-style: normal;
  font-weight: 400;
  line-height: 1.25rem;
  background-color: white;
  border-radius: 5px 0 0 5px;
  border: 1px solid white;
  padding: .8em .7em .8em .75em;
  margin-left: 1em;
  display: flex;
  justify-content: center;
  align-items: center;
}

.div-1-s1 img {
  padding-left: 0.6rem;
}

.div-2-s1 {
  display: flex;
}

.div-2-s1 input {
  font-family: 'Plus Jakarta Sans', sans-serif;
  font-weight: 400;
  font-size: 0.875rem;
  padding: .8em 0 .8em .9em;
  border: 1px solid white;
  line-height: 1.25rem;
  width: 100%;
  max-width: 100%;
}

#sent-icon {
  padding: .7em .5em .7em .5em;
  margin-right: 1em;
  border-radius: 0 5px 5px 0;
  border: 1px solid white;
  background-color: white;
}

<div class="search-button">
  <div class="div-1-s1">
    <span>All</span>
    <img src="t-icon.svg" alt="a svg icon" />
  </div>
  <div class="div-2-s1">
    <form action="#">
      <input type="text" id="label" placeholder="Search a 
             location">
    </form>
    <img src="f2-icon.svg" alt="a svg icon" id="sent-icon" />
  </div>
</div>

Answer 1

You just need to add width: 100% to the form as well

See this:

body {
  width: 100%;
}

.search-button {
  display: flex;
  justify-content: left;
  margin-left: .4em;
  margin-bottom: 1em;
  width: 100%;
}

.div-1-s1 {
  font-family: 'Plus Jakarta Sans', sans-serif;
  font-size: 0.875rem;
  font-style: normal;
  font-weight: 400;
  line-height: 1.25rem;
  background-color: white;
  border-radius: 5px 0 0 5px;
  border: 1px solid white;
  padding: .8em .7em .8em .75em;
  margin-left: 1em;
  display: flex;
  justify-content: center;
  align-items: center;
}

.div-1-s1 img {
  padding-left: 0.6rem;
}

.div-2-s1 {
  display: flex;
  width: 100%;
}

form {
  width: 100%;
}

.div-2-s1 input {
  font-family: 'Plus Jakarta Sans', sans-serif;
  font-weight: 400;
  font-size: 0.875rem;
  padding: .8em 0 .8em .9em;
  border: 1px solid black;
  /* change it back to white */
  line-height: 1.25rem;
  width: 100%;
}

#sent-icon {
  padding: .7em .5em .7em .5em;
  margin-right: 1em;
  border-radius: 0 5px 5px 0;
  border: 1px solid white;
  background-color: white;
}

<div class="search-button">
  <div class="div-1-s1">
    <span>All</span>
    <img src="t-icon.svg" alt="a svg icon" />
  </div>
  <div class="div-2-s1">
    <form action="#">
      <input type="text" id="label" placeholder="Search a location">
    </form>
    <img src="f2-icon.svg" alt="a svg icon" id="sent-icon" />
  </div>
</div>