Edited at

HTML email - Use Anchor as Button for Windows 10 Mail

More than 1 year has passed since last update.

Set CSS for inline HTML.

.btn {

border-radius: {{ RADIUS }};
background: {{ COLOR }};
}
.btn a {
border-radius: {{ RADIUS }};
border: solid 1px {{ COLOR }};
padding: 1em 1.5em;
color: #fff;
}

<table border="0" cellspacing="0" cellpadding="0" align="center">

<tr>
<td class="btn">
<a href="{{ URL }}">
{{ LABEL }}
</a>
</td>
</tr>
</table>

Anchor's display: block didn't work.

padding didn't work without set border.