<input type="number" min="1" max="5" value="8" id="range">

@import url("https://fonts.googleapis.com/css2?family=Exo:wght@600&display=swap");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --startColor: red;
}

body {
  width: 100vw;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  font-family: "Exo", Arial, sans-serif;
  background: linear-gradient(var(--startColor), #a24927, #1f23b3, #08124a);
  color: #fff;
}

input {
  min-width: 30vw;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  padding: 10px 15px;
  font-size: 2rem;
  border-radius: 3px;
  outline-offset: 3px;
}

input:out-of-range {
  color: var(--startColor);
  outline: 5px solid currentColor;
}

input:in-range {
  color: var(--startColor);
  outline: 5px solid currentColor;
}

const input = document.getElementById('range')
const themeColor = document.getElementById('theme__color')
const rootElement = document.documentElement

input.addEventListener('change', (etv) => {
  let val = etv.target.value
  let valMin = etv.target.min
  let valMax = etv.target.max
  
  
  if (val <= valMin || val >= valMax ){
    rootElement.style.setProperty('--startColor', 'red')
    themeColor.setAttribute("content", 'red')
  } else if (valMin < val && val < valMax){
    rootElement.style.setProperty('--startColor', 'green')
    themeColor.setAttribute("content", 'green')
  } else {
    console.log(val)
  }
  
})