Both are valid. It's your choice.

I prefer border:0 because it's shorter; I find that easier to read. You may find none more legible. We live in a world of very capable CSS post-processors so I'd recommend you use whatever you prefer and then run it through a "compressor". There's no holy war worth fighting here but Webpack → LESS → PostCSS → PurgeCSS is a good 2020 stack.

That all said, if you're hand-writing all your production CSS, I maintain —despite the grumbling in the comments— it does not hurt to be bandwidth conscious. Using border:0 will save an infinitesimal amount of bandwidth on its own, but if you make every byte count, you will make your website faster.

The CSS2 specs are here. These are extended in CSS3 but not in any way relevant to this.

'border'
    Value:      [ <border-width> || <border-style> || <'border-top-color'> ] | inherit
    Initial:    see individual properties
    Applies to:     all elements
    Inherited:      no
    Percentages:    N/A
    Media:      visual
    Computed value:     see individual properties 

You can use any combination of width, style and colour.
Here, 0 sets the width, none the style. They have the same rendering result: nothing is shown.

This short article covers the various bits of CSS shorthand you'll encounter in your day to day work.

https://www.w3.org/community/webed/wiki/CSS_shorthand_reference

Border

border allows you to set border width, style and, color.

UPDATE:

As @torazaburo pointed out it actually requires border: 0 none #ccc for it to be correct as well as adding border-radius: 0 as it's not part of the border shorthand.

#example {
  border: 0 none #ccc;
  border-bottom: 2px solid #ccc;
  border-radius: 0;
}

If it's not an issue that the following could take non-bottom border width and style from other rules in the cascade then this should be fine:

#example {
    border-bottom: 2px solid #ccc;
}

Produces the same CSS that you're wanting:

https://jsfiddle.net/betg5xue/5/

Use multiple text shadows:

text-shadow: 2px 0 #fff, -2px 0 #fff, 0 2px #fff, 0 -2px #fff,
             1px 1px #fff, -1px -1px #fff, 1px -1px #fff, -1px 1px #fff;

body {
  font-family: sans-serif;
  background: #222;
  color: darkred;
}

h1 {
  text-shadow: 2px 0 #fff, -2px 0 #fff, 0 2px #fff, 0 -2px #fff,
               1px 1px #fff, -1px -1px #fff, 1px -1px #fff, -1px 1px #fff;
}

<h1>test</h1>

Alternatively, you could use -webkit-text-stroke, which produces a slightly different result because it modifies the stroke width instead of adding additional shadows around the text. Despite the webkit prefix, it works in most browsers (including Firefox) as of 2022:

-webkit-text-stroke: 2px #fff;

body {
  font-family: sans-serif;
  background: #222;
  color: darkred;
}

h1 {
  -webkit-text-stroke: 2px #fff;
}

<h1>test</h1>

Also, read more at CSS-Tricks.

Just take the css that works for all tables, and add table.bordered before all of them:

table.bordered {
   border-collapse: collapse;
}
table.bordered td,  table.bordered th {
   border: 1px solid orange;
}

<table class="bordered">
    <tr> <td> ABC </td> <td> DEF </td> </tr> 
    <tr> <td> HIJ </td> <td> JLK </td> </tr>
</table>

<table>
    <tr> <td> ABC </td> <td> DEF </td> </tr> 
    <tr> <td> HIJ </td> <td> JLK </td> </tr>
</table>