mg <- ggplot(mtcars,aes(x=mpg,y=wt))+geom_point()
a=mg+theme_bw()+geom_text(aes(x=25,y=5),label='theme_bw',color='red',size=10)
b=mg+theme_classic()+geom_text(aes(x=25,y=5),label='theme_classic',color='red',size=10)
c=mg+theme_dark()+geom_text(aes(x=25,y=5),label='theme_dark',color='red',size=10)
d=mg+theme_light()+geom_text(aes(x=25,y=5),label='theme_light',color='red',size=10)
e=mg+theme_get()+geom_text(aes(x=25,y=5),label='theme_get',color='red',size=10)
f=mg+theme_linedraw()+geom_text(aes(x=25,y=5),label='theme_linedraw',color='red',size=10)
g=mg+theme_replace()+geom_text(aes(x=25,y=5),label='theme_replace',color='red',size=10)
h=mg+theme_minimal()+geom_text(aes(x=25,y=5),label='theme_minimal',color='red',size=10)
i=mg+theme_void()+geom_text(aes(x=25,y=5),label='theme_void',color='red',size=10)
grid.arrange(a,b,c,d,e,f,g,h,i,ncol=3)