How to add second line in the button with smaller text size

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;
}