Your CSS file mustn't be getting loaded somehow or you have an older version cached in your browser.
Your code works fine. Here it is working in a jsFiddle.
Try performing a hard refresh (generally CTRL+F5 on Windows, CMD+SHIFT+R on Mac) and ensuring your CSS file is located in the same directory as the HTML file you're trying to open.
Videos
Q1. What is the border in HTML?
Q3. How do I add borders in HTML?
Q2. Can I apply border effects using HTML?
Your CSS file mustn't be getting loaded somehow or you have an older version cached in your browser.
Your code works fine. Here it is working in a jsFiddle.
Try performing a hard refresh (generally CTRL+F5 on Windows, CMD+SHIFT+R on Mac) and ensuring your CSS file is located in the same directory as the HTML file you're trying to open.
Did you put the css file in a sub folder?
If so, you'll need to point to it:
<link rel="stylesheet" href="subfoldername/test.css" />
I assume you are doing something horrible like HTML email:
<center><table bgcolor="#ff00ff"></table></center>
<center>
<table border="1" cellspacing="0" cellpadding="0" width="200" align="center">
<tr>
<td background="http://www.yourdomain.com/email/images/background.jpg" align="left">
<!-- Stuff -->
</td>
</tr>
</table>
</center>
- http://www.email-standards.org/
- http://mailchimp.com/resources/guides/email-marketing-field-guide/
- http://www.1stwebdesigner.com/tutorials/ultimate-guide-html-emails/
The background attribute was never valid on table or td. Pretty sure the only thing the HTML 4 specification had background on was body. But I vaguely recall that it worked elsewhere and I think table cells was elsewhere--whether it works in Outlook you'll just have to test. bgcolor was valid all of those places...and is likely to work.
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.
They are equivalent in effect, pointing to different shortcuts:
border: 0;
//short for..
border-width: 0;
And the other..
border: none;
//short for...
border-style: none;
Both work, just pick one and go with it :)