prepare custom header setup

inc/custom-header.php

@@ -0,0 +1,36 @@
+<?php 
+function understrap_custom_header_setup() {
+
+	/**
+	 * Filter UnderStrap custom-header support arguments.
+	 *
+	 * @since UnderStrap 0.5.2
+	 *
+	 * @param array $args {
+	 *     An array of custom-header support arguments.
+	 *
+	 *     @type string $default-image     		Default image of the header.
+	 *     @type string $default_text_color     Default color of the header text.
+	 *     @type int    $width                  Width in pixels of the custom header image. Default 954.
+	 *     @type int    $height                 Height in pixels of the custom header image. Default 1300.
+	 *     @type string $wp-head-callback       Callback function used to styles the header image and text
+	 *                                          displayed on the blog.
+	 *     @type string $flex-height     		Flex support for height of header.
+	 * }
+	 */
+	add_theme_support( 'custom-header', apply_filters( 'understrap_custom_header_args', array(
+		'default-image'      => get_parent_theme_file_uri( '/img/header.jpg' ),
+		'width'              => 2000,
+		'height'             => 1200,
+		'flex-height'        => true
+	) ) );
+
+	register_default_headers( array(
+		'default-image' => array(
+			'url'           => '%s/img/header.jpg',
+			'thumbnail_url' => '%s/img/header.jpg',
+			'description'   => __( 'Default Header Image', 'understrap' ),
+		),
+	) );
+}
+add_action( 'after_setup_theme', 'understrap_custom_header_setup' );