I use KiCAD so I know it well. Unfortunately that site is in alpha and I am unable to zoom in to see the schematic clearly.

Use Ctrl+mousewheel to zoom.

(Unfortunately, it does not zoom on the cursor but on the center of the screen).

It seems that a person can also click to select an object on the board, and then use the "zoom to selection" button near the bottom-right of the viewport, to bring things up to a more-visible size and place [some of] them on-screen.

Vertical panning is then accomplished by rolling the scrollwheel. Horizontal scrolling can be accomplished by tilting the scrollwheel on a mouse that is so-equipped.

(Perhaps bizarrely, I was unable to discover any other way to pan.)

FWIW - On my laptop (track pad), I expected to click-drag or ctrl-drag to move it, but on a track pad it's two-finger swipe to move it left/right. then pinch zoom.

For me control-mousewheel zooms and shift-mousewheel pans horizontally.

pebkac error