Silica releases have been gradually getting new features and adjustments. Here are some high level changes listed.

5.0

Sailfish 5.0 polished support for display cutouts and better handling for rounded corners. E.g. the Page::cutoutMode and ApplicationWindow::defaultPageCutoutMode control how the Pages are handled.

4.0

Silica on Sailfish 4.x added gradual polish and adjustments.

• The text editors TextField and TextArea got some UI adjustments and support for filled background.
• C++ ImageProvider was added for allowing to use app specific graphics that are chosen for best size for the screen, and monochrome icons getting coloring based on current theme style.
• Notice component was added for making in-app notifications.
• PagedView added was providing full page component without moving to separate Pagestack Page.

The last of the 4.x series, Sailfish 4.6, added some preliminary support for displays with cutouts and heavily rounded corners.

During 4.x the Webkit based SilicaWebView component was dropped in favor of Gecko based webview component provided by Sailfish.WebView module.

3.0

The biggest new feature of Silica in Sailfish 3.x was the introduction of light themes / ambiences.

• The active theme scheme and various scheme specific color properties were added to the Theme.
• The Palette API can be used to access currently active palette
• SilicaItem and SilicaControl were added.

2.0

Sailfish 2.0 introduced big UI changes, adjusting the style and behavior of multiple components. The changes are described in their own page at What's New in Silica for Sailfish 2.0