library(ggplot2)
library(reshape2)

datime <- seq(as.POSIXct("2021-01-01"), as.POSIXct("2021-01-31"), by="d")
set.seed(5)
tmpout <- round(runif(31, 20, 35), 1)
tmpin <- tmpout + round(runif(31, -6, -5), 1)
temps <- data.frame(datime, tmpout, tmpin)

theme_set(theme_bw())

temps <- reshape2::melt(temps,id.vars='datime')

xlabel <- "Time"
ylabel <- expression(paste("Temperature (", ~degree~C, ")", sep=""))

g1 <- ggplot(aes(x=datime, y=value), data=temps) +
  geom_line(aes(color=variable), size=1) + 
  scale_colour_manual(name="Location",values=c("red","blue"),labels=c("Outside","Inside")) 
g2 <- scale_x_datetime(date_breaks="1 weeks", date_labels="%d %b %Y")
g3 <- g1 + g2 + labs(title="Indoor & Outdoor Temperatures\n800 Mindarie Road Pyap West SA 5333", x="Dates", y=ylabel)
l1 <- theme(legend.position=c(0.05,0.9), legend.key.width=unit(3,"line"), legend.text=element_text(size=14, face="bold"),
            legend.title=element_text(size=16, face="bold"), legend.title.align=0.5,
            legend.text.align=0.5, legend.spacing = unit(1, "cm"))
g3 + l1 + theme(axis.text.x=element_text(size=rel(1.4)),
                axis.title.x=element_text(size=20),
                axis.text.y=element_text(size=rel(1.4)),
                axis.title.y=element_text(size=20), plot.title=element_text(size=15,
                                                                            hjust=0.5))