Is it necessary to underline all the links in the interface?

I think the website would look much better if all of the links, ex. the header links like home/new post etc. And the post titles were not underlined.

You can still keep to underline links in text post and maybe what you can do is that only underline post titles that are links and not underline titles of text post.

Also, I think it's would be better to change the link colour something more fitting for the website (something like brown) instead of the default people.