Source

File: wp-admin/includes/class-wp-ms-themes-list-table.php

public function column_cb( $theme ) {
		$checkbox_id = 'checkbox_' . md5( $theme->get( 'Name' ) );
		?>
		<input type="checkbox" name="checked[]" value="<?php echo esc_attr( $theme->get_stylesheet() ); ?>" id="<?php echo $checkbox_id; ?>" />
		<label class="screen-reader-text" for="<?php echo $checkbox_id; ?>" ><?php _e( 'Select' ); ?>  <?php echo $theme->display( 'Name' ); ?></label>
		<?php
	}