Custom styles don't work, here's how to make them work

You have your css/styles.php include commented out. Hence, customizer choices for design won’t work.

There’s a better, actually reliable way to include that css. Change the contents of css/styles.php to be something like:

add_action( 'wp_head', 'uniform_add_css' );

function uniform_add_css() {
    $custom = '<style type="text/css">';
    // Theme color
    $uniform_theme_color = get_theme_mod( 'uniform_theme_color', '#a0ce4e' );
    if ( $uniform_theme_color != '#a0ce4e' ) {
        // removed all the specific rules for clarity
        //
        // ( wouldn't it be better to have a few classes
        // used throughout the theme?
        //
        //  .uniform-theme-color {
        //    color: $uniform_theme_color !important;
        // }
        // .uniform-theme-bgcolor {
        //    background-color: $uniform_theme_color !important;
        // }
        // and add them as appropriate to elements? This block of
        // seems really fragile and a pain to maintain )
    }
    $uniform_custom_css = get_theme_mod( 'uniform_custom_css', '' );
    $custom .= $uniform_custom_css;
    $custom .= '</style>';
    echo $custom;
}