regsiter pattern in the block theme

function.php

<?php

register_block_pattern(
    'starter/custom-button-pattern',
    array(
        'title'       => __( 'Custom buttons', 'starter' ),
        'description' => _x( 'Two horizontal buttons, the left button is filled in, and the right button is outlined.', 'Block pattern description', 'starter' ),
        'categories'  => array( 'buttons' ),
        'content'     => '<!-- wp:buttons -->
        <div class="wp-block-buttons"><!-- wp:button {"backgroundColor":"vivid-green-cyan"} -->
        <div class="wp-block-button"><a class="wp-block-button__link has-vivid-green-cyan-background-color has-background wp-element-button">Custom button</a></div>
        <!-- /wp:button --></div>
        <!-- /wp:buttons -->',
    )
);