Sometimes people ask about translucent titlebars and borders. I’ve just discovered Stardock’s Curtains, which came out in 2020.

This changes the title bar, buttons and border for most windows. There’s a reasonable range of ready-made ones available, with more downloadable and on sites like Wincustomize.
Here it is with one of many available skin options, one which has reasonable button design, slightly rounded corners, and a degree of transparency. The transparency is both an option and slightly adjustable by changing the saturation of the colour chosen. Both a range of colours and the full colour picker is available for the title bar and border.
Title bar and border- translucency and style in current builds-1.png

Here’s Groove:

Title bar and border- translucency and style in current builds-groove.png
Aeroglass vs Curtains
Not everyone’s happy with the simple square frames and lack of transparency that comes as standard. I’ve been using Aeroglass, which functions not as a skin but with existing Windows features. Unfortunately it’s not been updated for well over a year– a new version is needed at least for each major Windows Build, and was last compatible with a particular build of 1903 and I believe of 1909, so had to look for a change.
Curtains – notes
Resource use, it runs a service and a process, taking around 1Mb of RAM.
Title bar and border- translucency and style in current builds-2.png

Price: For US customers it’s $10.99, but £9.99 in the UK, which makes it more expensive here. To get the US price, use a US proxy using a browser without the site’s cookie set. 30 day trial.

Inactive vs active: Unfortunately it seems there’s no difference in the title bar colour, but the buttons and text in the inactive window are dimmer.
Works well with Firefox and Thunderbird, not applicable to Chrome. Ok with old Edge, not tried Edge Chromium.
Unlike the more comprehensive WindowBlinds, Curtains does not allow the scrollbar to be modified, which some would like.

Border Width
Winaero’s free tweaker includes a convenient option for setting the border padding and width.

Title bar and border- translucency and style in current builds-5.png