Hi there,
there isn’t an option in the block editor for this.
You would need to use HTML to create the Button eg.
<a class="button two-line-button" href="the_url">The first line of text<span>The second line</span></a>
We can the add some styles to that button:
/* Button style */
a.two-line-button {
background-color: #0366d6;
color: #fff;
padding: 15px 20px;
display: block;
text-align: center;
}
a.two-line-button:hover {
background-color: #222;
}
/* Second line style */
a.two-line-button span {
display: block;
font-size: 12px;
}