When doing this, you don't have to worry a bit about the Blogger-theme ... no-one will ever see it.
Login to your Blogger-account and choose the blog you want to redirect.
Then, click on the 'Edit HTML' button:
When you see the source code of the theme, add a 'meta refresh' tag to the HEAD-section, as in the example in the screenshot:
Note: when you have saved this change, you won't be able to preview new blog posts from within Blogger... because the preview will redirect you immediately to your website.
Some things to consider:
When editing the source code or when you write a blog post, you might get the warning from Blogger that you are mixing http and https content. So ...
1) your own domain is HTTP and you load images or other things from a HTTPS domain, like from blogger.com : no problem
2) your own domain is HTTPS and you load images or other things from a HTTP domain : problem, needs to be avoided!
3) when your domain is reachable via both HTTP and HTTPS, always redirect HTTP to HTTPS. This can be done via editing the Apache VirtualHost file and add a permanentRedirect rule, or add rewriteCond rules to a .htaccess file in your root website folder : search Google for rewrite rules
So, now that you know a bit more, you can ignore the warnings from Google because you know why the warning pops up.
Furthermore, in the case of adding the META-tag, the warning is irrelevant, because you redirect any visitor immediately to your website.
Last but not least: if you load things form other domains than yours, install Privacy Badger (from EFF) and test your site with it. You’ll see what gets blocked and that’s what visitors, who also use a plugin like this, might experience too.
