HTML Div border not showing

Solution 1:

The default value of border-style is none. You need to set a different value for a border to appear.

#container-border {
  border-width: 2px;
  border-color: red;
  border-style: dashed;
}

<div id="container-border">
  ...
</div>

You can use the shortcode for border, which contains color, width AND style (which you are missing right now):

#container-border {
  border: 2px solid red;
}

You have to set the rule "border-style" to see the border

#container-border {
  border-width: 2px;
  border-color: red;
  border-style:solid;
}

<div id="container-border">
  ...
</div>