Aligning form elements to bottom of flexbox unit, but keep text at the top

Question

I'm very new to this, but am trying to put together a page that is a little above my pay grade so far, and it seems to be working well enough, but I cannot seem to figure out how to get the 'input' to stay at the bottom of the flex box and keep the text and image at the top. I have the feeling it's an hierarchy or parent/child issue, but I can't seem to get my brain around it. SO far I have tried everything I know how, but here's where I'm at now...

I've created a separate "DIV ID" with its own set of rules for the input which state that the input)s) should: "align-self: flex-end;" Still not working.. Any ideas would be very much appreciated!

body {
  background-color: #faf8ed;
}

.header {
  background-color: black;
  padding: 21px;
  border-radius: 25px;
}

img {
  max-width: 100%;
  flex-wrap: wrap;
  margin-left: auto;
  margin-right: auto;
  margin-top: auto;
  margin-bottom: auto;
  display: block;
}

h1 {
  font-family: 'Modak', cursive;
  font-variant: small-caps;
  letter-spacing: 2px;
  text-align: center;
  font-weight: normal;
}

p {
  font-family: 'Amatic SC', cursive;
  font-weight: bold;
  font-size: 16px;
}

#container1 {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: center;
  height: 100%;
  align-items: stretch;
  padding-top: 37px;
}

#one {
  border: 1px solid beige;
  font-family: Arial;
  font-size: .75em;
  padding: 10px;
  width: 200px;
  margin-left: 7px;
  margin-right: 7px;
  margin-top: 7px;
  margin-bottom: 7px;
  border-radius: 25px;
  background-color: beige;
}

#bottom {
  display: flex;
  align-self: flex-end;
}

.zoom {
  transition: transform .3s;
  /* Animation */
  margin: 0 auto;
}

#quantity {
  display: flex;
  font-family: Arial;
  font-size: 1.5em;
  font-family: 'Amatic SC', cursive;
  font-weight: bold;
  text-align: center;
  padding-right: 3px;
}

#buy {
  display: flex;
  font-family: Arial;
  font-size: 1.5em;
  font-family: 'Amatic SC', cursive;
  font-weight: bold;
  border-radius: 7px;
}

<div id="container1">
  <div id="one" class="zoom">
    <h1>KING GIZZARD ROCKS!</h1>
    <img src="tshirt_2.jpg">
    <p>
      This is the text for this shirt!
    </p>
    <form action="">
      <div id="bottom">
        <label for="quantity" id="quantity">Quantity:</label>
        <input type="number" name="quantity" min="1" max="30" placeholder="0">
        <br>
        <input type="submit" id="buy" value="BUY">
    </div><!--bottom-->
    </form>
    </div><!--one-->
    <div> <!--container-->        

Answer 1

align-self: flex-end would work if the parent was a flex container (i.e., the parent had display: flex or display: inline-flex). But in this case, the parent (form) is not a flex container, so the children will ignore flex properties.

Flex properties only work between parent and child elements. Read more about the scope of flex layout here: Proper use of flex properties when nesting flex containers

Without changing your HTML (which could be made more efficient), you could achieve the desired layout by making the #one element a flex container in column direction, and applying auto margins to the form element.

In the example below I've also removed a lot of unnecessary code (at least for demo purposes).

#container1 {
  display: flex;
  /* flex-direction: row; */
  /* flex-wrap: wrap; */
  justify-content: center;
  height: 100vh; /* adjustment */
  /* align-items: stretch; */
  /* padding-top: 37px; */
}

/* .header {
  background-color: black;
  padding: 21px;
  border-radius: 25px;
} */

#one {
  /* border: 1px solid beige; */
  font-family: Arial;
  font-size: .75em;
  padding: 10px;
  width: 200px;
  /* margin-left: 7px; */
  /* margin-right: 7px; */
  /* margin-top: 7px; */
  /* margin-bottom: 7px; */
  /* border-radius: 25px; */
  background-color: beige;
  display: flex; /* new */
  flex-direction: column; /* new */  
}

img {
  max-width: 100%;
  /* flex-wrap: wrap; */
  /* margin-left: auto; */
  /* margin-right: auto; */
  /* margin-top: auto; */
  /* margin-bottom: auto; */
  /* display: block; */
}

h1 {
  font-family: 'Modak', cursive;
  font-variant: small-caps;
  letter-spacing: 2px;
  text-align: center;
  font-weight: normal;
  margin-top: 0; /* new */
}

p {
  font-family: 'Amatic SC', cursive;
  font-weight: bold;
  font-size: 16px;
}

form {
  margin-top: auto; /* new */
}

#bottom {
  display: flex;
  /* align-self: flex-end; */
}

.zoom {
  transition: transform .3s;
  /* Animation */
  margin: 0 auto;
}

#quantity {
  display: flex;
  font-family: Arial;
  font-size: 1.5em;
  font-family: 'Amatic SC', cursive;
  font-weight: bold;
  text-align: center;
  padding-right: 3px;
}


#buy {
  display: flex;
  font-family: Arial;
  font-size: 1.5em;
  font-family: 'Amatic SC', cursive;
  font-weight: bold;
  border-radius: 7px;
}

body {
  background-color: #faf8ed;
  margin: 0; /* new */
}

* {
  box-sizing: border-box;
}

<div id="container1">
  <div id="one" class="zoom">
    <h1>KING GIZZARD ROCKS!</h1>
    <img src="http://i.imgur.com/60PVLis.png">
    <p>This is the text for this shirt!</p>
    <form action="">
      <div id="bottom">
        <label for="quantity" id="quantity">Quantity:</label>
        <input type="number" name="quantity" min="1" max="30" placeholder="0">
        <br>
        <input type="submit" id="buy" value="BUY">
      </div><!--bottom-->
    </form>
    </div><!--one-->
  <div><!--container-->

jsFiddle demo