Diagonal border line with (inline) CSS - html

Question

I would like to have a white diagonal stripe with css. I have tried something but I don't get it work. I will put the link in here as well so you can have a look.
Is there anyone who can help me out?
<table width="600" border="0" cellspacing="0" cellpadding="0" align="center" class="wrapper-section-one editable">
<tbody>
<tr>
<td>
<table width="100%" border="0" cellspacing="0" cellpadding="0" align="center">
<tbody>
<tr>
<td>
<table width="300" border="0" cellspacing="0" cellpadding="0" align="left" style="background: black; outline: none; outline-offset: 2px; border: 10px solid white; height: 90px;
background-image: linear-gradient(to bottom right, black, black 50%, white 50%, white); " class="wrapper-section-one editable bg-editable" data-selector="table.bg-editable">
<tbody>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="text-align:center;">
<img src="images/blank.gif" width="1" height="27" alt="" title="">
</td>
</tr>
<tr>
<td height="20">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:14px;color:#ffffff;text-transform:uppercase;text-align:center;font-weight:bold;">
<br/>
</td>
</tr>
<tr>
<td height="10">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:13px;color:#ffffff;text-transform:capitalize;text-align:center;">
</td>
</tr>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
</tbody>
</table>
<table width="300" border="0" cellspacing="0" cellpadding="0" align="right" style="background: #c11717; outline: none; outline-offset: 2px; border: 10px solid white;" class="wrapper-section-one editable bg-editable" data-selector="table.bg-editable">
<tbody>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="text-align:center;">
<img src="images/mark.png" width="17" height="27" alt="" style="display:initial;" data-selector="div.editable img">
</td>
</tr>
<tr>
<td height="20">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:14px;color:#ffffff; text-transform:uppercase;text-align:center;font-weight:bold;">
Kop 1
</td>
</tr>
<tr>
<td height="10">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:13px;color:#ffffff; text-transform:capitalize;text-align:center;">
Tekst 1
</td>
</tr>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
</tbody>
</table>
</td>
</tr>
<tr>
<td>
<table width="300" border="0" cellspacing="0" cellpadding="0" align="left" style="background: #c11717; outline: none; outline-offset: 2px; border: 10px solid white;" class="wrapper-section-one editable bg-editable" data-selector="table.bg-editable">
<tbody>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="text-align:center;">
<img src="images/icon_date.png" width="27" height="27" alt="" style="display:initial;" data-selector="div.editable img">
</td>
</tr>
<tr>
<td height="20">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:14px;color:#ffffff; text-transform:uppercase;text-align:center;font-weight:bold;">
Kop 2
</td>
</tr>
<tr>
<td height="10">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:13px;color:#ffffff; text-transform:capitalize;text-align:center;">
Tekst 2
</td>
</tr>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
</tbody>
</table>
<table width="300" border="0" cellspacing="0" cellpadding="0" align="right" style="background: black; outline: none; outline-offset: 2px;border: 10px solid white;" class="wrapper-section-one editable bg-editable" data-selector="table.bg-editable">
<tbody>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="text-align:center;">
<img src="images/wclock.png" width="24" height="27" alt="" style="display:initial;" data-selector="div.editable img">
</td>
</tr>
<tr>
<td height="20">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:14px;color:#ffffff;text-transform:uppercase;text-align:center;font-weight:bold;">
Kop 3
</td>
</tr>
<tr>
<td height="10">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
<tr>
<td style="font-size:13px;color:#ffffff;text-transform:capitalize;text-align:center;">
Tekst 3
</td>
</tr>
<tr>
<td height="50">
<img src="images/blank.gif" width="1" height="1" alt="" title="">
</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>

Answer 1

Here's a copy of your image using the linear-gradient CSS approach. MUCH less markup required :)
div#wrapper {
float: left;
width: 220px;
height: 220px;
margin: 0px;
}
div#wrapper div {
width: 100px;
height: 100px;
float: left;
background: red;
margin: 0px 10px 10px 0px;
}
div#wrapper #d1 {
background-image: repeating-linear-gradient(145deg, black, black 60px, white 60px, white 80px);
}
div#wrapper #d4 {
background: black;
}
<div id="wrapper">
<div id="d1"></div>
<div id="d2"></div>
<div id="d3"></div>
<div id="d4"></div>
</div>

Answer 2

Here is my approach to get the result exactly as in your example image link, but it doesn't work for emails.
.box {
position: relative;
margin: 0 15px 15px 0;
width: 100px;
height: 100px;
float: left;
}
.cf {
clear: left;
}
.box--red {
background-color: #ff0000;
}
.box--black {
background-color: #000000;
}
.box--split:before {
content: "";
position: absolute;
border-top: 50px solid #000;
border-right: 50px solid transparent;
border-left: 50px solid #000;
border-bottom: 50px solid transparent;
box-sizing: border-box;
}
.box--split:after {
content: "";
position: absolute;
right: 0;
bottom: 0;
display: block;
box-sizing: border-box;
border-right: 40px solid #000;
border-top: 40px solid transparent;
border-bottom: 40px solid #000;
border-left: 40px solid transparent;
}
<div class="box box--split">
</div>
<div class="box box--red">
</div>
<div class="box box--red cf">
</div>
<div class="box box--black">
</div>