Hello Ben,
The files must have the following contents:
header.php
<?php
// =============================================================================
// HEADER.PHP
// -----------------------------------------------------------------------------
// The site header.
// =============================================================================
x_get_view( 'header', 'base' );
base.php
<?php
// =============================================================================
// VIEWS/HEADER/BASE.PHP
// -----------------------------------------------------------------------------
// Declares the DOCTYPE for the site, includes the <head>, opens the <body>
// element as well as the .x-root <div> and .x-site <div>.
// =============================================================================
$x_root_atts = x_atts( apply_filters( 'x_root_atts', array( 'id' => 'x-root', 'class' => 'x-root' ) ) );
$x_site_atts = x_atts( apply_filters( 'x_site_atts', array( 'id' => 'x-site', 'class' => 'x-site site' ) ) );
?>
<!DOCTYPE html>
<html class="no-js" <?php language_attributes(); ?>>
<head>
<?php wp_head(); ?>
</head>
<body <?php body_class(); ?>>
<?php wp_body_open(); ?>
<?php do_action( 'x_after_body_begin' ); ?>
<div <?php echo $x_root_atts; ?>>
<?php do_action( 'x_before_site_begin' ); ?>
<div <?php echo $x_site_atts; ?>>
<?php do_action( 'x_after_site_begin' ); ?>
What are you trying to insert in the header? You may be adding it in the wrong file. Please provide the HTML code or the script that you need to add to your header so that we can advise you on the proper way of adding it to your site header.
Best Regards.