Hey Leslye,
I’ve double-checked – the file should be working :) its name is indeed supposed to be “header-functions.php” – I’ve named the archive differently so as to give an idea of its purpose. Could you please double-check if you’ve uploaded the files into the correct folder (/wp-content/themes/Ikebana/), and the original file has been replaced? If it still doesn’t work, please download this file, unzip it, and upload into the same folder.
Please let me know of the results!
Best,
Andrew / Satori Studio