My Suggestions for the Upvote/Downvote System:

The current system only allows you to upvote/downvote comments once, and you are unable to change that decision. I feel like there are some flaws with this, so I have two main suggestions.

Change it so that users can change the decision about upvoting/downvoting.

Rationale: Many people mis-click the upvote/downvote button, and cause them to accidentally downvote/upvote a certain blog/comment. Also, people change their minds on their decisions for upvoting/downvoting, so it would be beneficial if you could change your decision.

Change it so that blogs/comments show both the amount of upvotes and downvotes.

Rationale: When a blog/comment shows both upvotes and downvotes would show a more holistic story. It would also show the amount of people that have inputted their opinions on the blog/comment. Typically, a small sample size is less representative than a bigger one.

These are just my suggestions. I understand that these suggestions would probably be incredibly hard to implement to the actual Codeforces platform.