Are there any risks as far as loss of ranking is concerned with css design changes?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Yasser Mohamed: Hi guys, ; I am currently getting my WP site rebuilt as it had a lot of coding issues resulting from a (poorly)highly modified theme. ; I just want to know what I should be careful of when it comes to launching my new site - especially from an SEO point of view. ; I am not changing my CMS or my domain, basically just the theme and the hosting and I am going to try and keep the current URLs intact. ; I am very nervous as I am currently on page 1 of Google, in both organic and local for a high competition keyword phrase and I don't want to lose this ranking. ; I have done all my own on site optimisation and even though my site has been poorly coded I have managed to rank very well. ; I am rebuilding my site as it has some CSS issues which affect the way it appears on different screens and browsers so my bounce rate is a bit high and I want to make it give it a better end user experience. ; Are there any risks as far as loss of ranking is concerned with this rebuild? ; How can I minimise them and what do I need to communicate to my developer to ensure a smooth transition?
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  RACHIT GUPTA: You need to taking care about your hosting migration. Most of times, during migration it happens that your old files still exist on old server and ; website is running on new as well as old server both. So, be take care and confirm that after taking backup all files from old server, delete all files from old server, otherwise duplicate content and mirror website issue raise. During migration, the possibility of ranking fluctuation also happens. See, Google reads website content not your website theme but yes structure plays important role. You need to taking care about URL structuring, it should be the same and no one page is missing in new one as well as canonical issue.
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  Yasser Mohamed: Thank you +RACHIT GUPTA that is very good advice.
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  Devin Peterson: Agreed with +RACHIT GUPTA ;, now I don't have any additional advice, but in my experience, a site redesign usually lead to better results in terms of traffic and site usage. Generally the redesigns were drastic improvements though. It often included improving page speed, removing unnecessary links and banners etc that were distracting and ugly and clogging up the conversion funnel so to speak as well as managing categorization better, so as long as your changes are indeed improvements and not just experiments or guesswork, then I would not be worried about any losses.
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  Yasser Mohamed: Thanks +Devin Peterson . ; Yes the aim of this redesign is to fix some issues with coding, improve speed/load times and create a better end user experience and end up with a much cleaner website but without altering the structure so drastically that we lose ranking.
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  Devin Peterson: I think in short I would be confident to say you will not lose traffic due to structural changes unless there were errors being made along the way.
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  Yasser Mohamed: Good to hear thanks +Devin Peterson ;
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  Edwin Jonk: From the expert panel in this weeks SEO Questions hangout on air on 01:25:04 into the YouTube video: https://dumbseoquestions.com/q/are_there_any_risks_as_far_as_loss_of_ranking_is_concerned_with_css_design_changes +Yasser Mohamed
  
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