For the blogspot test code, here's how it handles according to these different tests.
Validate HTML ❌
Validate CSS ❌
Page works | Viewport | Zoom | Font
Chrome ✅ ❌ ❌ ❌
Firefox ✅ ❌ ❌ ❌
Safari ❌ ❌ ❌ ❌
Edge ✅ ❌ ✅ ✅
IE 11 ✅ ❌ ✅ ✅
I really wanted to give more ticks , but your code failed in every category of the tests.
The test page fails to work in Safari, partly because the
<style> tags inside of the
<body> are ignored. There's information in the next section on how to fix that.
The HTML validation of your blogspot page fails for several reasons specific to Blogspot.
Ignoring the failures that are due to using Blogspot, the
<style> tags aren't valid where you've placed them.
Here are Blogspot instructions to Change your blog’s design using HTML or CSS.
Important note: CSS does not go in your HTML code. Even with Blogger, it remains separate.
You have an illegal CSS parameter.
Side panel becomes partly obscured below a viewport width of 1000 pixels, and is fully obscured at 720 pixels. Users are used to scrolling vertically. It is bad to force users to scroll horizontally.
It is important that viewports be usable down to at least 768 pixels wide. Yours becomes problematic below 1000 pixels, which is bad and needs to be fixed. If your code was free of problems down to 720 pixels, it would gain a tick.
Better solutions result in the information still being visible down to viewports of 320 pixels, as is the case on cellphones.
Chrome links break their formatting at 110%, 90%, 80%, 75%, 33%, 25%
Firefox links break at all zoom levels below 100%, that is, 90%, 80%, 65%, 50%, 30%
Safari links are broken at 100%, and are also broken at all possible zoom levels.
Chrome: Users preferred font-size settings are completely ignored
Firefox: Users preferred font-size settings are completely ignored
Safari: Users preferred font-size settings are completely ignored
All in all, your code still has a lot of work that needs to be done, before it passes any of these tests.
I recommend that you take on the advice of the experts here, for what you are currently doing doesn't seem to be working for you.