Shrinking images without losing quality

Question

So I tried rebuilding the Twitter Tweet bar, and everything is okay - however, the small image next to the tweet bar (which is your own profile picture on Twitter, in case you're interested) has a really bad quality. But on the Twitter website, the quality remains good (no matter how small the image is).

Goal / Question: How can I make a small image maintain and keep the good quality?

Here my CSS code (nothing special):

.tweetpic {
            width: 50px;
            height: 50px;
            object-fit: cover;
            vertical-align: middle;
            border-radius: 25px;
            margin-right: 5px;
        }