Adjust faces for ElScreen
Improve the readability of let bindings in setup-window-system-configuration
Set the frame font for a current session

When we set the frame font by (set-frame-font fsn), the font
configuration will be lost after calling 'load-theme' interactively.
By passing a non-nil value as the third parameter of set-frame-font, the
configuration will be applied to future frames.
This seems to solve the above problem.
Use setq instead of setq-default because variables are not buffer-local