Help with Riemann sum graph

[ThatOneCalculator]

I'm pretty new to Typst (been using for a few days) and really new to CeTZ (been trying it out tonight). I'm trying to plot a graph of f(x) = 16 - x^2 and its left-hand Riemann sum (from [0,6], 6 intervals). I feel like I'm close, but I can't quite work out how to fix this.
Here's my current code:

#canvas(length: 0.4in, {
  let f = x => 16 - x * x
  let barColor = color.green
  for i in (0, 1, 2, 3, 4, 5) {
    let height = f(i)
    if (height < 0) {
      barColor = color.red
    }
    draw.fill(barColor.lighten(69%).darken(8%))
    draw.rect(
      (i, 1),
      (i+1, height),
    )
  }
  
  plot.plot(size: (8, 6),
    x-grid: true,
    y-grid: true,
    x-tick-step: 1,
    y-tick-step: 4,
    {
      plot.add(
        domain: (0, 6),
        x => f(x))
    })
})

Below is the graph with the for loop commented out, and below that is what I want it to look like (done with Desmos)

[ThatOneCalculator]

I solved it! Now onto #393

#canvas(length: 0.4in, {
  // Function
  let f = x => 16 - x * x

  // Plot
  plot.plot(size: (6, 6),
    x-grid: true,
    y-grid: true,
    x-tick-step: 1,
    y-tick-step: 4,
    {
      plot.add(
        domain: (0, 6),
        x => f(x))
    }
  )

  // Left-hand Riemann sum
  let barColor = color.green
  let fixedOffset = 3.34
  for i in (0, 1, 2, 3, 4, 5) {
    let height = f(i)
    if (f(i) < 0) {
      barColor = color.red
    }
    //draw.fill(barColor.lighten(70%).darken(8%))
    draw.stroke(barColor.darken(30%))
    draw.rect(
      (i, fixedOffset),
      (i + 1, (height / 6) + fixedOffset),
    )
  }
})

[ThatOneCalculator]

Styled it a bit nicer

#align(center)[#canvas(length: 0.4in, {
  // Function
  let f = x => 16 - x * x

  // Plot
  plot.plot(size: (6, 6),
    x-grid: true,
    y-grid: true,
    axis-style: "school-book",
    x-tick-step: 1,
    y-tick-step: 4,
    padding: 10pt,
    {
      plot.add(
        domain: (0, 6),
        x => f(x))
    }
  )

  // Left-hand Riemann sum
  let barColor = color.green
  let fixedOffset = 10/3
  for i in (0, 1, 2, 3, 4, 5) {
    let height = f(i)
    if (f(i) < 0) {
      barColor = color.red
    }
    draw.fill(rgb(barColor.lighten(70%).darken(8%).to-hex() + "66"))
    draw.stroke(barColor.darken(30%))
    draw.rect(
      (i, fixedOffset),
      (i + 1, (height / 6) + fixedOffset),
    )
  }
})]