Having trouble changing Header Image Size and Font Size in Yoko Child Theme

Hello,

I just moved from using wordpress.com to my own self-hosted site, and I’m trying to make some adjustments to my blog’s theme. I am currently using Yoko and really like it, except for the Header. I want to make the header image smaller, and I would like to try changing the font of the blog title to see if there is something better.

I have been doing research and found that I need to child theme. I created a child theme directory, and so far was able to change the font size of the blog title using the style.css file. I don’t know how to change the actual font though…

I tried creating a functions.php file but can’t figure out what to put there to change the header size. Most of the tutorials I found use one of the twenty-something themes and the header info is really obvious in the functions.php file but I can’t find similar info the Yoko functions.php file.

I only see one section in the header.php file that defines the header size:

<?php
			// The header image. If single post w/thumbnail that's big enough, show it
			if ( is_singular() && current_theme_supports( 'post-thumbnails' ) && has_post_thumbnail( $post->ID ) && ( $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'post-thumbnail' ) ) && $image[1] >= HEADER_IMAGE_WIDTH ) :
				echo get_the_post_thumbnail( $post->ID , array( 1102, 350 ), array( 'class' => 'headerimage' ) );
			elseif ( get_header_image() ) : ?>
				<img src="<?php header_image(); ?>" class="headerimage" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo get_custom_header()->height; ?>>" alt="" />
		<?php
			endif;

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So I tried creating a header.php file with this info and changed 350 to 300, but when I uploaded it, the contents of my header.php in the child theme directory showed up as a mess of html on the top of my blog.

Sorry this is so long, but I’m hoping the details makes it easier for me to get help. I’m pretty new this and haven’t used php before.

TIA