The style.css was updated to be responsive and work with the new Genesis 1.8 version (it was new at the time). The functions.php, home.php, and page_portfolio was updated. Pretty much everything has been updated, but if you made customizations to your style.css file and a new update appears, you can use a site like – http://www.diffchecker.com/ to compare which part of the code has changed.
Child themes aren’t really that easy to update when dealing with css, especially when Legacy was made responsive and updated to work with Genesis 1.8…..there was a lot that needed to be changed. The link above should help you compare changes. If you just want the responsive features, you could start by adding the responsive code at the bottom of the css and then make the adjustments as needed…..but only do this if you know how to create responsive code, otherwise I’d recommend hiring a developer to do this for you as it could take a lot of work.
Also, you could maybe setup a local install of the new Legacy version, and then just add in your navigation code (replacing what you have). If this seems like too much work I’m sure you could hire someone to do this for you quickly. I know Wes (the creator) could get this done fast, and you could also check the StudioPress recommended developers as well.
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