study(title="Relative Strength Index", shorttitle="RSI")
src = close, len = input(14, minval=1, title="Length")
up = rma(max(change(src), 0), len)

down = rma(-min(change(src), 0), len)
rsi = down == 0 ? 100 : up == 0 ? 0 : 100 - (100 / (1 + up / down))
plot(rsi, color=black)
band1 = hline(70)
band0 = hline(30)
fill(band1, band0, color=purple, transp=90)
hline(50, linestyle = dotted, color= black, title= "Center")
sma=sma(rsi, 9)
plot(sma(rsi, 9), color= red)
upper = hline(70)
lower = hline(30)
fill (upper, lower)
s1=rsi[1] > sma[1] and rsi < sma and rsi[1]>70
s2=rsi[1] < sma[1] and rsi > sma and rsi[1]<20
bgcolor(s1 ? red : na, transp=30)
bgcolor(s2 ? green : na, transp=30)