My ConvertKit newsletter template...

index.html

<style>
#message-content {
	margin: 0;
	padding: 0 18px 10px;
	max-width: 640px;
}
#message-content img {
	max-width: 100%; height: auto;
}
#message-footer {
	border-top:1px solid #e5e5e5;
	padding-top:16px;
	padding-bottom:16px;
}
p {
	margin: 1em 0;
	padding: 0;
}

#message-content table{
	border-collapse:collapse;
	mso-table-lspace:0;
	mso-table-rspace:0;
}
#message-content table{
	border-spacing:0;
	margin-bottom:1em;
	max-width:100%;
	width:100%;
}
#message-content th,#message-content td{
	text-align:left;
	padding:.5em;
}
#message-content th{
	border-bottom:2px solid #e5e5e5;
	font-weight:bold;
	vertical-align:bottom;
}
#message-content td{
	border-top:1px solid #e5e5e5;
	vertical-align:top;
}

pre,code{
	font-family:monospace;
	font-size:inherit;
}
code{
	color:#dd1144;
	word-wrap:break-word;
}
pre{
	background-color: #1f252f;
	border: 1px solid #ffffff;
	border-radius: 8px;
	color: #ffffff;
	padding:13px;
	tab-size:4;
	white-space:pre-wrap;
	word-break:break-all;
}
pre code{
	background-color:transparent;
	border:0;
	color:inherit;
	padding:0;
}
</style>
<div id="message-content">
{{ message_content }}
<div id="message-footer">
<p><strong>Don't want to get these emails?</strong> Totally cool. <a href="{{ subscriber_preferences_url }}">Update your subscriber preferences.</a></p>
<p>You can also <a href="{{ unsubscribe_url }}">unsubscribe from all emails</a> from me.</p>

{{ address }}
<br>
</div>
</div>