There appears to be a white line above the image in Gmail app on IOS in dark mode.
I've tried many solutions regarding this but could not remove the white line/space.
img[class="visual"] {
width: 100% !important;
height: auto !important;
text-align: center;
margin: 0 auto;
}<tr>
<td bgcolor="transparent" valign="middle">
<table cellpadding="0" cellspacing="0" border="0" class="content" align="center" width="640">
<tr>
<td bgcolor="transparent" align="center" valign="top" style="width: 640px;">
<a href="TBC" target="_blank" alias="Banner"><img src="https://via.placeholder.com/150.jpg" width="640" height="250" style="display: block; border: none; max-height: 250px;" border="0" alt="Banner" class="visual" /></a>
</td>
</tr>
</table>
</td>
</tr>