Rebuild only css files correponding to a changed less file

Makefile

css_files := $(shell find . -name '*.css' -type f -print)
less_files := $(patsubst %.css,%.less,$(css_files))

show_less:
	@echo $(less_files)

less: $(less_files)

$(less_files): %.less: %.css
	@echo "Building $@"
	@touch $@