Global zoom

In the top right of the Polypane window is a slider that lets you zoom out all panes simultaneously. This way you can make all your panes fit the current screen. You can slide to zoom in and out, or you can press ctrl and scroll to zoom in and out. The global zoom is stored per view mode and per tab.

To go back to 100% zoom, you can press cmd/ctrl 0.

You can also click the percentage shown to fill in a specific value.

Zoom to fit

With shift cmd/ctrl 0 you can zoom out such that all panes are visible.

Page zoom and pane zoom

You can also zoom individual panes with pane zoom and zoom in the content of a pane (like regular browsers) with page zoom.