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HTML 

              
                <canvas id="canvas" width="100" height="100"></canvas>
!

CSS 

              
                body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: #000;
}

#canvas {
  width: 100vmin;
  height: 100vmin;
  vertical-align: middle;
  image-rendering: pixelated;
  cursor: pointer;
}
!

JS 

              
                const { min, max, round, floor, abs, sqrt } = Math
const random = (x = 1) => Math.random() * x
const rgb = (...values) => `rgb(${values.join(',')})`
const rgba = (...values) => `rgba(${values.join(',')})`
const distance = (x1, y1, x2, y2) => sqrt(
  abs(x1 - x2)**2 +
  abs(y1 - y2)**2
)

const Sky = (() => {
  const State = {
    pos: [0, 0],
    stars: [],
    moonPos: []
  }

  const speed = 0.05

  function updatePosition() {
    State.pos[0] -= speed
    State.pos[1] += speed
  }

  function reset() {
    State.pos = [0, 0]
    State.stars = []
    State.moonPos = []
  }

  function spaceColor(size) {
    const moonAltitude = size / 2 - State.pos[1] + moonSize
    return rgb(
      min(max(0, moonAltitude), 12.5),
      min(max(5, moonAltitude), 20),
      min(max(10, moonAltitude), 25)
    )
  }

  function drawSpace(ctx, size) {
    ctx.fillStyle = spaceColor(size)
    ctx.fillRect(0, 0, size, size / 2)
    let px = size * -1
    while (px++ < size * size) {
      let pxX = px % (size * 2)
      let pxY = floor(px / (size * 2))
      const moonX = State.moonPos[0] + moonSize / 2 - 1
      const moonY = State.moonPos[1] + moonSize / 2
      const moonDistance = distance(moonX, moonY, pxX, pxY)
      if (moonDistance < moonSize * 1.75) {
        ctx.fillStyle = rgba(255, 255, 255, .05)
        ctx.fillRect(
          State.pos[0] + pxX,
          State.pos[1] + pxY,
          1,
          1
        )
      }
      if (moonDistance < moonSize) {
        ctx.fillStyle = rgba(255, 255, 255, .1)
        ctx.fillRect(
          State.pos[0] + pxX,
          State.pos[1] + pxY,
          1,
          1
        )
      }
    }
  }

  const starCount = () => 1000 + round(random(2000))
  const starColor = () => rgba(
    255,
    200 + round(random(55)),
    200 + round(random(20)),
    random()
  )

  function generateStars(size) {
    if (State.stars.length) {
      return
    }
    let count = starCount()
    while (count-- > 0) {
      State.stars.push([
        round(random(size * 8)),
        round(random(size * 8)) * -1 + size
      ])
    }
  }

  function drawStars(ctx, size) {
    let star = State.stars.length
    while (star-- > 0) {
      ctx.fillStyle = starColor()
      ctx.fillRect(
        State.stars[star][0] + State.pos[0],
        State.stars[star][1] + State.pos[1],
        1,
        1
      )
    }
  }

  const moonSize = 10
  const moonColors = {
    0: 'transparent',
    1: rgb(210, 210, 210),
    2: rgb(255, 255, 255),
    3: rgb(120, 120, 120),
  }

  const moonBitmap = [
    0, 0, 0, 0, 1, 1, 0, 0, 0, 0,
    0, 0, 1, 2, 1, 1, 1, 1, 0, 0,
    0, 1, 1, 1, 1, 3, 3, 3, 1, 0,
    0, 1, 3, 3, 1, 1, 3, 3, 1, 0,
    1, 3, 3, 3, 3, 2, 1, 3, 1, 1,
    1, 1, 3, 3, 3, 1, 1, 1, 1, 1,
    0, 1, 1, 3, 1, 2, 1, 1, 1, 0,
    0, 1, 1, 1, 2, 2, 2, 1, 1, 0,
    0, 0, 1, 1, 1, 1, 1, 1, 0, 0,
    0, 0, 0, 0, 1, 1, 0, 0, 0, 0
  ]

  function placeMoon(size) {
    if (State.moonPos.length) {
      return
    }
    State.moonPos[0] = size / 3 + round(random(size / 2))
    State.moonPos[1] = moonSize + round(random(size / 10))
  }

  function drawMoon(ctx, size) {
    let bit = 0
    while (bit++ < moonBitmap.length - 1) {
      const bitPos = [
        State.moonPos[0] + State.pos[0] + bit % moonSize,
        State.moonPos[1] + State.pos[1] + floor(bit / moonSize)
      ]
      ctx.fillStyle = moonColors[moonBitmap[bit]]
      ctx.fillRect(bitPos[0], bitPos[1], 1, 1)
    }
  }

  return Object.freeze({
    draw(ctx, size) {
      generateStars(size)
      placeMoon(size)
      drawSpace(ctx, size)
      drawStars(ctx, size)
      drawMoon(ctx, size)
      updatePosition()
      return {
        x: State.pos[0],
        y: State.pos[1],
        moonPos: {
          x: State.pos[0] + State.moonPos[0] + moonSize / 2 - 1,
          y: State.pos[1] + State.moonPos[1] + moonSize / 2
        },
        moonSize
      }
    },
    reset
  })
})()

const Sea = (() => {
  function seaColor(size, moonAlt) {
    const alt = size / 2 - moonAlt
    const minGreen = 10 + round(random(10))
    const maxGreen = 10 + round(random(25))
    const minBlue = 20 + round(random(50))
    const maxBlue = 50 + round(random() > .9 ? random(120) : random(50))
    return rgb(
      0,
      max(maxGreen + min(alt * 3, 0), minGreen),
      max(maxBlue + min(alt * 3, 0), minBlue)
    )
  }

  return Object.freeze({
    draw(ctx, size, { x: skyX, y: skyY, moonPos, moonSize, stars }) {
      let x = 0
      let y = 50
      while (x * y < size * size) {
        const xSize = round(random(5))
        ctx.fillStyle = seaColor(size, skyY + moonSize)
        ctx.fillRect(x, y, xSize, 1)
        const verticalShine = min(
          1.25,
          size / 2 - moonPos.y + moonSize / 2
        )
        if (moonPos.x + moonSize >= x && moonPos.x - moonSize <= x) {
          ctx.fillStyle = rgba(
            255,
            255,
            255,
            verticalShine / 10
          )
          ctx.fillRect(x, y, xSize, 1)
        }

        const verticalNarrowShine = min(
          0.75,
          size / 2 - moonPos.y + moonSize / 2
        )
        if (moonPos.x + moonSize / 2 >= x && moonPos.x - moonSize / 2 <= x) {
          ctx.fillStyle = rgba(
            255,
            255,
            255,
            verticalNarrowShine / 10
          )
          ctx.fillRect(x, y, xSize, 1)
        }

        const circularShine = min(
          2.5,
          size / 2 - moonPos.y + moonSize
        )
        const moonDistance = distance(
          moonPos.x,
          moonPos.y,
          x, y
        )
        if (moonDistance < moonSize * 2) {
          ctx.fillStyle = rgba(
            255,
            255,
            255,
            circularShine / 10
          )
          ctx.fillRect(x, y, xSize, 1)
        }

        x += xSize
        if (x >= size) {
          x = 0
          y++
        }
      }
    }
  })
})()

function draw() {
  ctx.clearRect(0, 0, size, size)
  const skyState = Sky.draw(ctx, size)
  Sea.draw(ctx, size, skyState)
  requestAnimationFrame(draw)
}

function reset() {
  Sky.reset()
}

canvas.addEventListener('click', reset)
const ctx = canvas.getContext('2d')
const size = canvas.width
draw()
!
999px

Console