Logo got bigger (visually) resulting in quality loss

Hi
I have uploaded my logo which is 200x200px.
I have noticed that it has been resized visulally (it got bigger), though after downloading it preserves its original dimensions. This resulted in qulaity loss (I previewed the website using Firefox 35.0.1).
Why does it happen? How can I prevent it from being resized (upsized and eventually downsized)?
I use left sidebar.

Thanks
A.

• This topic was modified 9 years, 7 months ago by Autostopowicz.