Resize current pane height(holding second key is optional)
panes
// what it does
Ctrl+b Ctrl+Up / Ctrl+b Ctrl+Down run resize-pane -U / -D, growing or shrinking the active pane one row per press. The bindings carry the -r (repeat) flag, so within repeat-time you can keep tapping Ctrl+Up / Ctrl+Down without re-pressing the prefix. The Ctrl on the arrow is what selects resize — plain prefix+arrow is bound to select-pane.
// shortcut
Ctrl + b↑
Ctrl + bCtrl + ↑
Ctrl + b↓
Ctrl + bCtrl + ↓
// gotcha
Don't drop the Ctrl: Ctrl+b Up (no Ctrl on the arrow) runs select-pane -U and switches panes instead of resizing. The repeat window is governed by repeat-time (default 500ms); pause too long and the next keypress goes to the shell rather than resizing. A pane also can't grow past its neighbor's minimum height, and a later next-layout wipes the manual size.