Margin property question

HTML & CSS
1

Can somebody explain to me what

margin : 15px auto;

does?
Thank you very much!

2

The margin (and padding) has a shortcut declaration that lets you set the top, right, bottom, and left sizes in one single declaration (rather than setting margin-top, margin-right, etc.). If you set just two sizes, it defines the top and bottom, then the sides.

The following declarations all have the same result:

div {
  margin: 15px auto; /* top/bottom, then right/left */
}

div {
  margin: 15px auto 15px auto; /* top right bottom left */
}

/* The long version... */
div {
  margin-top: 15px;
  margin-right: auto;
  margin-bottom: 15px;
  margin-left: auto;
}

As for what “auto” does, it just tells the browser to figure it out. You would usually do this to make a block element centered horizontally inside another, for example.

3

Thank you very much for your explanation.Clear and concise!