style.css

:root {
  --color: #4400ff;
  --eraser: 1rem;
}

* {
  margin: 0 auto;
  padding: 0;
}
html {
  box-sizing: border-box;
  font-size: 62.5%;
}
body {
  position: relative;
}
.controls {
  position: absolute;
  top: 50%;
  left: 0;
  transform: translate(0, -50%);
  background-color: #ddd;
  display: flex;
  flex-direction: column;
  color: var(--color);
  justify-content: space-around;
  font-size: 1.5rem;
  font-family: sans-serif;
  font-weight: 600;
  padding: 0 0.7rem;
  border-radius: 0 2rem 2rem 0;
}
.control__group {
  display: flex;
  flex-direction: column;
  margin: 1rem auto;
}

.color {
  border: none;
  border-radius: 50%;
  width: 2rem;
  height: 2rem;
  background: #ddd;
  overflow: hidden;
}

input[type="number"] {
  border: none;
  width: 4rem;
  border: 2px solid var(--color);
}

.eraser {
  width: var(--eraser);
  height: var(--eraser);
  background: #fff;
  margin: 1rem auto;
  border-radius: 50%;
}

input[type="range"] {
  width: 6rem;
  height: 1rem;
  background: transparent;
  cursor: pointer;
  margin: 0.5rem auto;
}
input[type="range"],
input[type="range"]::-webkit-slider-runnable-track,
input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
}
input[type="range"]::-webkit-slider-runnable-track {
  height: 0.4rem;
  background: #aaa;
}
input[type="range"]::-webkit-slider-thumb {
  position: relative;
  height: 1.5rem;
  width: 1.5rem;
  background: steelblue;
  border-radius: 50%;
  border: 2px solid white;
  transform: translateY(-0.6rem);
}