I have some design requirements for an email template where I have two "challenges":
- two columns need to flip to one column
- some visible border lines need to be switched from vertical to horizontal
The following shows how it should look (2 columns on the left for desktop, 1 column on the right for mobile):
The whole email is based on responsive tables and the two-column part is implemented as follows right now:
<table cellpadding="5" cellspacing="0"
style="background-color:#F6F6F6; font-size: 14px; color:#58595b; width:100%; border-collapse:collapse;">
<tr><td align="center" valign="top" height="10" colspan=2 style="line-height: 10px; font-size: 10px;"> </td></tr>
<tr>
<td valign="top" style="border-right: 1.5px solid; border-color: #d0d0d0; padding-right:40px; text-align:right; width:42%; vertical-align:top;">
Start point
</td>
<td valign="top" style="padding-left:40px; vertical-align:top;">
<strong>Fri, January 12, 2023 12:00</strong>
<br />
Harbour, Seatown
</td>
</tr>
<tr><td align="center" valign="top" height="10" colspan=2 style="line-height: 10px; font-size: 10px;"> </td></tr>
<tr>
<td valign="top" style="border-right: 1.5px solid; border-color: #d0d0d0; padding-right:40px; text-align:right; width:42%; vertical-align:top;">
End point
</td>
<td valign="top" style="padding-left:40px; vertical-align:top;">
<strong>So, January 18, 2023 10:00</strong>
<br />
Central Station, Capital
</td>
</tr>
<tr><td align="center" valign="top" height="10" colspan=2 style="line-height: 10px; font-size: 10px;"> </td></tr>
</table>
I tried the approach with having a left and a right table (explained here) but the problem is that I do not use fixed widths.
How could I achieve the required design with a responsive mail template?

You will need to use the technique as outlined in the link, but if you want to use percentages instead of fixed widths, then use
width="50%".This is because the technique works on the basic fundamentals of HTML, that if a block doesn't fit in the space available, it will automatically shift underneath.
So to enable the stacking without a fixed pixel width, you will need to add a
@mediaquery to force the stacking (otherwise it would not stack).e.g.
(The article you link to is a bit outdated: don't use
[class=...], just write it out normally. Gmail may strip the entire<style>section if it doesn't like something in it, and this is one of those things it doesn't like.)I prefer an override (max-width, and !important) because you want everything possible inline, and only to use embedded styles where strictly necessary.
But that's also why it's best to use a fixed pixel width, because some email clients do not respect your embedded styles (styles in the
<head>). GANGA emails (one form of Gmail account) fall into this category. Those email clients would not stack even though they may need to, if you fully rely on the@mediaquery for the stacking.To override the border, put a style on the
<td>, and reference it in the@mediaquery, e.g.As one doesn't have the same border structure (they don't both need border-bottom), one of the
<td>s will need a different class. Here, I'm expecting the first one, i.e.<td class="border border-top">.