Use wp_head to dinamically generate CSS

wp-head-css.php

<?php
add_action( 'wp_head', 'dolly_print_styles' );
function dolly_print_styles() {
    $options = get_option( 'my-options' );
    ?>
        <style>
            .my-class {
                background-color:<?php echo $options['background-color']; ?>;
                font-size:<?php echo $options['font-size']; ?>px;
            }
        </style>
    <?php
}