Justify-self is not working when I want to align content in the center [duplicate]

Question

I am having to use auto margins to align content in the center of the page.

div {
  background: #121212;
  font-size: 100%;
  display: flex;
}
a {
  color: #fff;
  padding: 2%;
  display: inline-block;
  background: linear-gradient(180deg, rgba(18, 18, 18, 0.8) 0%, rgba(18, 18, 18, 0.5) 66.66%), url('https://cml.sad.ukrd.com/image/714544.png');
  background-size: cover;
  background-position: top;
  white-space: nowrap;
  font-size: 18px;
}
img {
  height: 100%;
  width: auto;
  display: flex;
  align-self: center;
  max-height: 50px;
  margin: 0 auto;
  /* fails justify-self: center; */
}

<div>
  <a href="#">⟵ Some Text Goes Here</a>
  <img src="https://cml.sad.ukrd.com/image/714824.png">
</div>

I want to discover how to position the blocks image in the centre of the parent div. The div already has another <a> child, which is pushing the block image slightly out of the centre. The div parent is a flexbox, and I assumed having a justify-self: center rule would work, but apparently not, hence why I've had to use margin: 0 auto, which doesn't competely centre align it anyway.

How can the block image be in the dead centre of the parent div?

Answer 1

justify-self: center; is a property of css grid, not flex. https://css-tricks.com/snippets/css/complete-guide-grid/#prop-justify-self

Answer 2

You could take the a element out of normal flow positioning it relative to it's parent div.

See below for a demo and the documentation is in the comments:

div {
  background: #121212;
  font-size: 100%;
  display: flex;
  position: relative; /*Make sure the anchor tag is positioned relative to this div*/
}
a {
  color: #fff;
/*   padding: 2%; remove the padding */
  display: flex; /*Make the element a flex container to center it's contents*/
  justify-content: center;
  align-items: center;
  background: linear-gradient(180deg, rgba(18, 18, 18, 0.8) 0%, rgba(18, 18, 18, 0.5) 66.66%), url('https://cml.sad.ukrd.com/image/714544.png');
  background-size: cover;
  background-position: top;
  white-space: nowrap;
  font-size: 18px;
/* Position the element absolutely taking it out of the normal flow of the document   */
  position: absolute;
  top: 0;
  left: 0;
  height: 100%;
}
img {
  height: 100%;
  width: auto;
  display: flex;
  align-self: center;
  max-height: 50px;
  margin: 0 auto;
  /* fails justify-self: center; */
}

<div>
  <a href="#">⟵ Some Text Goes Here</a>
  <img src="https://cml.sad.ukrd.com/image/714824.png">
</div>