styles.css

:root {
  --yangColor: #d8c21e;
  --yinColor: #111111;
  --background: rgba(0, 0, 0, 0.3);
}

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

.canvas {
  font-family: 'Poppins', sans-serif;
  width: 100%;
  height: 100vh;
  background-color: var(--yinColor);
}

.container {
  position: absolute;
  transform: translate(-50%, -50%);
  top: 50%;
  left: 50%;
  width: 80vw;
}

.countdown {
  display: flex;
  justify-content: space-around;
  gap: 10px;
}

.title {
  font-size: 30px;
  color: var(--yangColor);
  text-align: center;
  margin-bottom: 20px;
}

.box {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-evenly;
  font-size: 16px;
  width: 28vmin;
  height: 28vmin;
  border: 4px solid var(--yangColor);
  box-shadow: 15px 15px 30px var(--background);
}

.box::after {
  content: '';
  position: absolute;
  background-color: rgba(143, 158, 10, 0.3);
  height: 100%;
  width: 50%;
  left: 0;
}

.digit {
  color: var(--yangColor);
  background-color: transparent;
  display: block;
  height: 100%;
  width: 100%;
  display: grid;
  place-items: center;
  font-size: 5em;
  font-weight: 600;
  z-index: 1;
}

.text {
  color: var(--yinColor);
  font-size: 1.2em;
  font-weight: 400;
  background-color: var(--yangColor);
  display: block;
  width: 100%;
  text-align: center;
  padding: 0.5em 0;
  z-index: 1;
}

@media screen and (max-width: 768px) {
  .title {
    font-size: 24px;
  }
  .countdown {
    width: 100%;
    flex-wrap: wrap;
    gap: 30px;
  }
  .box {
    width: calc(50% - 40px);
    height: 30vmin;
    font-size: 12px;
  }
}

@media screen and (max-width: 768px) {
  .container {
    width: 90vw;
    height: 100%;
  }
  .title {
    margin-top: 15px;
    font-size: 16px;
  }
  .box {
    min-height: auto;
    font-size: 8px;
  }
  .text {
    font-size: 1.8em;
  }
}

@media screen and (max-width: 768px) and (orientation: portrait) {
  .box {
    width: 100%;
  }
}

@media screen and (max-width: 768px) and (orientation: landscape) {
  .box {
    width: 45%;
  }
}