source: mavix-resort/1.0/inc/custom-header.php

<?php
/**
 * Sample implementation of the Custom Header feature
 *
 * You can add an optional custom header image to header.php like so ...
 *
        <?php the_header_image_tag(); ?>
 *
 * @link https://developer.wordpress.org/themes/functionality/custom-headers/
 *
 * @package Mavix Resort
 */

/**
 * Set up the WordPress core custom header feature.
 *
 * @uses mavix_resort_header_style()
 */
function mavix_resort_custom_header_setup() {
        add_theme_support( 'custom-header', apply_filters( 'mavix_resort_custom_header_args', array(
                'default-image'          => '',
                'default-text-color'     => '000000',
                'width'                  => 1920,
                'height'                 => 1080,
                'flex-height'            => true,
                'wp-head-callback'       => 'mavix_resort_header_style',
        ) ) );

        // Register default headers.
        register_default_headers( array(
                'default-banner' => array(
                        'url'           => '%s/assets/images/default-header.jpg',
                        'thumbnail_url' => '%s/assets/images/default-header.jpg',
                        'description'   => esc_html_x( 'Default Banner', 'header image description', 'mavix-resort' ),
                ),

        ) );
}
add_action( 'after_setup_theme', 'mavix_resort_custom_header_setup' );

function mavix_resort_header_style() {
        $mavix_resort_header_text_color = get_header_textcolor();

        /*
         * If no custom options for text are set, let's bail.
         * get_header_textcolor() options: Any hex value, 'blank' to hide text. Default: HEADER_TEXTCOLOR.
         */
        if ( get_theme_support( 'custom-header', 'default-text-color' ) === $mavix_resort_header_text_color ) {
                return;
        }

        // If we get this far, we have custom styles. Let's do this.
        // Has the text been hidden?
        if ( ! display_header_text() ) :
                $mavix_resort_custom_css = ".site-title,
                .site-description {
                        position: absolute;
                        clip: rect(1px, 1px, 1px, 1px);
                }";
        // If the user has set a custom color for the text use that.
        else :
                $mavix_resort_custom_css = ".site-title a {
                        color: #" . esc_attr( $mavix_resort_header_text_color ) . "}";
        endif;
        wp_add_inline_style( 'mavix-resort-style', $mavix_resort_custom_css );
}
add_action( 'wp_enqueue_scripts', 'mavix_resort_header_style' );