App.css

@import '@radix-ui/colors/blackA.css';
@import '@radix-ui/colors/violet.css';

.SliderRoot {
  position: relative;
  display: flex;
  align-items: center;
  user-select: none;
  touch-action: none;
  width: 200px;
  height: 20px;
}

.SliderTrack {
  background-color: var(--blackA10);
  position: relative;
  flex-grow: 1;
  border-radius: 9999px;
  height: 3px;
}

.SliderRange {
  position: absolute;
  background-color: white;
  border-radius: 9999px;
  height: 100%;
}

.SliderThumb {
  display: block;
  width: 20px;
  height: 20px;
  background-color: white;
  box-shadow: 0 2px 10px var(--blackA7);
  border-radius: 10px;
}
.SliderThumb:hover {
  background-color: var(--violet3);
}
.SliderThumb:focus {
  outline: none;
  box-shadow: 0 0 0 5px var(--blackA8);
}

App.tsx

import './App.css';
import * as Slider from '@radix-ui/react-slider';
import { useState } from 'react';

function App() {
  const currentMilitaryTime = new Date().getHours() * 100;
  const [time, setTime] = useState([currentMilitaryTime]);

  function fromMilitaryTime(militaryTime: number) {
    const atLeastFourLong = militaryTime.toString().padStart(4, '0');
    const hours = atLeastFourLong.slice(0, 2);
    const minutes = Math.floor(
      (parseInt(atLeastFourLong.slice(2, 4)) / 100) * 60,
    );
    return `${hours}:${minutes.toString().padEnd(2, '0')}`;
  }

  return (
    <div className='App'>
      <Slider.Root
        className='SliderRoot'
        defaultValue={[currentMilitaryTime]}
        max={2400}
        min={100}
        step={50}
        aria-label='Time'
        value={time}
        onValueChange={setTime}
      >
        <Slider.Track className='SliderTrack'>
          <Slider.Range className='SliderRange' />
        </Slider.Track>
        <Slider.Thumb className='SliderThumb' />
      </Slider.Root>
      {fromMilitaryTime(time[0])}
    </div>
  );
}

export default App;