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HTML

              
                
<div style="margin-bottom: 2rem;">
  <label for="set-aqi">Set AQI:</label><input type="range" id="set-aqi" min="0" max="500" value="10">
</div>
<div class="gauge">
  <div role="meter" aria-valuemin="0" aria-valuemax="500" aria-labelledby="meter-label">
    <div class="dial"><span class="aqi-num"></span><span>AQI</span><div class="arrow"></div></div>
  </div>
  <label class="label" id="meter-label">10 Minute Average US EPA PM2.5 AQI</label>
</div>

              
            
!

CSS

              
                body {
  background-color: darkslategray;
  font-family: 'Open Sans', sans-serif;
  color: #fff;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.gauge {
  display: inline-block;
}

.gauge > div[role=meter] {
  border-radius: 8rem 8rem 0 0;
  border: 1px solid black;
  width: 16rem;
  height: 8rem;
  background-color: black;
  position: relative;
  overflow: hidden;
  background: conic-gradient(from 0deg at 50% 100%,
                              red 30deg, #8f3f97 30deg 60deg,
                              #7e0023 60deg 91deg, transparent 91deg 269deg,
                              #00e400 269deg 300deg, #ffff00 300deg 330deg,
                              #ff7e00 330deg 360deg);
}

.gauge > label {
  font-size: 14px;
  text-align: center;
  background-color: black;
  padding: .2rem 0;
  display: block;
}

.dial {
  background-color: #00ff00;
  transition: background-color 1s, color .25s;
  border-radius: 10rem 10rem 0 0;
  width: 70%;
  height: 70%;
  display: flex;
  flex-direction: column;
  align-content: center;
  justify-content: center;
  position: absolute;
  bottom: 0;
  left: 15%;
  z-index: 2;
  overflow: hidden;
  box-shadow: 0px 0px 0px 1rem #000;
  border-bottom: none;
  box-sizing: border-box;
  color: #000;
}

.dial.white {
  color: #fff;
}

.dial > span {
  text-align: center;
  font-family: sans-serif;
}

.dial > .arrow {
  position: absolute;
  left: calc(50% - .25rem);
  bottom: 0;
  width: .5rem;
  height: calc(100% + 1px);
  background-color: transparent;
  transform-origin: bottom center;
  transform: rotate(-90deg);
  transition: transform 1s;
}

.dial > .arrow:after {
  content: "";
  border-left: .5rem solid transparent;
  border-right: .5rem solid transparent;
  border-top: .5rem solid #000;
  position: absolute;
  left: calc(50% - .5rem);
  top: 0;
  width: 0;
  height: 0;
  transition: border-color .25s;
}

.dial.white > .arrow:after {
  border-top-color: #fff;
}

.aqi-num {
  font-weight: bold;
  font-size: 120%;
  margin-top: 1.25rem;
}

@media (forced-colors: active) {
  .dial {
    border: 2px solid black;
    border-bottom: none;
  }
  
  .gauge > div[role=meter] {
    border-width: 2px;
    border-bottom: none;
  }
  
  .gauge > label {
    border: 2px solid black;
  }
}

              
            
!

JS

              
                  function setDial(aqi) {
    let angle = getAQIDialAngle(aqi);
    let [bg, white] = getAQIColor(aqi);

    let meter = document.querySelector(".gauge > div[role=meter]");
    let dial = meter.querySelector(".dial");
    meter.setAttribute("aria-valuenow", aqi);
    meter.setAttribute("aria-valuetext", aqi);
    dial.querySelector(".aqi-num").textContent = aqi;
    dial.querySelector(".arrow").style.transform = `rotate(${angle - 90}deg)`;
    dial.style.backgroundColor = bg;
    dial.classList.toggle("white", white);
  }


function getAQIDialAngle(aqi) {
  if (aqi >= 301) {
    return Math.min((aqi - 301) / 200 * 30 + 150, 180);
  } else if (aqi >= 201) {
    return (aqi - 201) / 100 * 30 + 120;
  } else if (aqi >= 151) {
    return (aqi - 151) / 50 * 30 + 90;
  } else if (aqi >= 101) {
    return (aqi - 101) / 50 * 30 + 60;
  } else if (aqi >= 51) {
    return (aqi - 51) / 50 * 30 + 30;
  } else if (aqi >= 0) {
    return aqi / 50 * 30;
  } else {
    return 0;
  }
}

function getAQIColor(aqi) {
  function combineColors(c1, c2, bias) {
    return c1.map((c, i) => ((c * (1 - bias)) + (c2[i] * bias)));
  }

  function stringifyColor(c) {
    return `rgb(${c})`;
  }

  function calculateColors(c1, c2, bias) {
    let bg = combineColors(c1, c2, bias);
    let white = ((bg[0] * 299) + (bg[1] * 587) + (bg[2] * 114)) / 1000 < 128;
    return [stringifyColor(bg), white];
  }

  const aqiColorMap = [
    [0, [0, 255, 0]],
    [50, [255, 255, 0]],
    [100, [255, 126, 0]],
    [150, [255, 0, 0]],
    [200, [143, 63, 151]],
    [300, [126, 0, 35]]
  ];

  for (let i in aqiColorMap) {
    let [target, color] = aqiColorMap[i];
    if (target > aqi) {
      if (i == 0) {
        return calculateColors(color, color, 1);
      }

      let [prevTarget, prevColor] = aqiColorMap[i - 1];
      return calculateColors(prevColor, color, (aqi - prevTarget) / (target - prevTarget));
    }
  }

  let [, color] = aqiColorMap[aqiColorMap.length - 1];
  return calculateColors(color, color, 1);
}

let range = document.getElementById("set-aqi");
setDial(range.value);

range.addEventListener("change", evt => {
  setDial(evt.target.value);
});
              
            
!
999px

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