Nothing happens when I do these

[foryoung2018]

Alt + Left Click: Move window
Alt + Right Click: Resize window
Alt + F4: Close window
Alt + Tab: Switch window

ctrl+shift grabs mouse and keyboard showing in Xephyr window title

[little-populus]

If you are using a keyboard which has a numLock key, note that key binding will be viewed as Mod1Mask | ... | Mod2Mask instead, all thing you need to do is to turn off NumLock or just add Mask like this
XGrabButton(
display_,
Button1,
Mod1Mask | Mod2Mask, //you should add Mod2Mask in every grab function if don't want to turn off NumLock
w,
false,
ButtonPressMask | ButtonReleaseMask | ButtonMotionMask,
GrabModeAsync,
GrabModeAsync,
None,
None);