df <- data.frame(a=c(2,4,8), b=c(5, 10, 15))
  
plot = ggplot(df, aes(x = a, y = b)) + geom_point() + geom_line()
  
#output
plot

df <- data.frame(a=c(2,4,8),b=c(5, 10, 15))
  
plot + theme(panel.grid.major = element_blank(), 
               panel.grid.minor = element_blank())

df <- data.frame(a=c(2,4,8),b=c(5, 10, 15))
  
# theme_bw() function
plot + theme_bw()

df <- data.frame(a=c(2,4,8),b=c(5, 10, 15))
  
plot + theme(panel.background = element_blank())