Resize Split View

How

With two apps open in Split View, locate the vertical divider between them
Place your finger on the divider and drag left or right
Release when each app has the amount of space you want

Try this

Open Split View with Safari and Notes. Drag the divider to give Safari two-thirds of the screen, then drag it back to an even 50/50 split.

Why it works

Adjust how much screen space each app gets.

Drag the line.