where’s the code error in that?

Now there are 10 errors ??

Re your questions:
Any lists should start with <ul> or <ol>.
Learn: https://www.w3schools.com/html/html_lists.asp

The things in your sidebar, like the links (and the Link Categories – which are NOT the same as post categories!!!) are coded in the sidebar.php of the theme.

But how can the mistake come from the sidebar.php file since I haven’t modified it, it’s the original one that came with the theme?

What theme are you using? Sometimes themes get whacked in the design process…. just depends on how “good” the theme author is….

In the thread where this was first being discussed you stated you had edited the sidebar.php,

“The files I modified are style.css, header.php, comments.php, sidebar.php, footer.php …”

His site is here, vkaryl, https://raphaella.co.kr/blog/ and notice the footer. ??

It’s fSpring.

Hmmm. Thanks, whooami. Guess I missed the earlier thread….

flush, I’m not familiar with the theme used, perhaps you need to contact the theme author. Failing that, maybe you should start with the theme from scratch, reuploading the files and making your changes one at a time until you get to the break-point (where the validator starts borking….)

https://www.ads-software.com/support/topic/84949?replies=8

Beats me. All I modified was the style.css
Other than that I had to install a few lines of script, an image map in the header.php
I have an old blog using a more basic fSpring theme, the validator doesn’t show these ul errors.
Can changes in the style.css file create a problem like this or is it totally unrelated?