style.css

* {
  margin: 0;
  padding: 0;
  font-size: 62.5%;
  box-sizing: border-box;
  transition: all 2s;
}

.container {
  --background: #f1f1f1;
  --clock-background: white;
  --shadow-color: gray;
  --second-hand: red;
  --hands: black;
  --dot: white;
}

.container.dark-mode {
  --background: #1f1d36;
  --clock-background: black;
  --shadow-color: antiquewhite;
  --second-hand: red;
  --hands: white;
  --dot: black;
}

.container {
  background-color: var(--background);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.clock {
  position: relative;
  display: block;
  height: 30rem;
  width: 30rem;
  background: var(--clock-background);
  border-radius: 50%;
  border: 0.5rem solid var(--clock-background);
  box-shadow: inset 0.2rem 0.3rem 0.8rem 0 var(--shadow-color);
  transform: rotate(180deg);
}

.hand {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  animation: none;
}

.second {
  width: 0;
  transform-origin: top;
  border: 3px var(--second-hand) solid;
  height: 40%;
  border-radius: 0.2rem;
  box-shadow: 0 0.5rem 3rem gray;
  animation: none;
}

.minute {
  width: 0;
  border-radius: 0.2rem;
  background-color: var(--hands);
  transform-origin: top;
  border: 2px var(--hands) solid;
  height: 45%;
  box-shadow: 0 0.5rem 3rem var(--shadow-color);
}

.hour {
  border-radius: 0.2rem;
  width: 0;
  background-color: var(--hands);
  transform-origin: top;
  border: 3px var(--hands) solid;
  height: 30%;
  transform: rotate(90deg);
  box-shadow: 0 0.5rem 3rem var(--shadow-color);
}

.dot {
  width: 2rem;
  height: 2rem;
  border-radius: 50%;
  background-color: var(--clock-background);
  box-shadow: inset 0 0 0.8rem var(--shadow-color);
}

.toggle {
  font-size: 2rem;
  margin-top: 5rem;
  padding: 1rem;
  border: 2px var(--hands) solid;
  border-radius: 0.3rem;
  background: var(--clock-background);
  color: var(--hands);
}