Fade transition of logo change in the nav bar

Hey,

I've implemented the following code to change the header logo (located in the nav bar), when you scroll down the page.

/* Change logo on scroll */

.shrink .header-title-logo img {
visibility: hidden;
transition: all 0s;
}
.shrink .header-title-logo a {
background-image: url(LINK);
background-size: contain;
background-repeat: no-repeat;
background-position: center center;
transition: all 2s;
}

/* Change logo on scroll */

However, I want the two logo versions to fade into each other, so it's not a sudden transition. 

Also, the nav bar judders/expands ever so slightly, when you initially scroll. Is there a way to fix that?

Any help is much appreciated!

password: chartica

Thanks

website: https://chartica-test.squarespace.com