:root {
  --gray-color: #404a65;
  --black-color: #35383f;
  --blue-color: #1f6fb0;
  --white-color: #ecedf0;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-size: 16px;
}

body {
  font-family: "Kanit", sans-serif;

  background-color: var(--gray-color);
}

.author-info {
  font-size: 14px;
  text-align: center;
  color: rgb(55, 65, 81);
  color: var(--white-color);
  margin-top: 56px;
}

.author-info a {
  text-decoration: none;
}

.container {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  margin-top: 30px;
}

#heading {
  text-shadow: 2px 2px 0px #222, 3px 3px 0px #222, 4px 4px 0px #222;
  -webkit-text-stroke-width: 2px;
  -webkit-text-stroke-color: #35383f;
  font-size: 4rem;
  color: var(--white-color);
  font-weight: 700;
}

#sub_heading {
  font-size: 1.5rem;
  color: var(--white-color);
  font-weight: 600;
  margin-top: 8px;
}

#random_button {
  background-color: var(--blue-color);
  color: var(--white-color);
  font-size: 1.25rem;
  font-weight: 600;
  box-shadow: 0px 4px 0px 0px #23649b;
  border: none;
  border-radius: 8px;
  padding: 12px 36px;
  text-transform: uppercase;
  cursor: pointer;
  margin-top: 48px;
}

#random_button:hover {
  background-color: #23649b;
  transition: 0.1s ease-in-out;
}

#random_button:disabled {
  background-color: gray;
  color: #aaa;
  cursor: not-allowed;
  opacity: 0.6;
}

#coin_container {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  margin-top: 56px;
  gap: 36px;
}

#coin_description {
  color: var(--white-color);
  font-size: 1.5rem;
}

#coin {
  height: 150px;
  width: 150px;
  position: relative;
  -webkit-transform-style: preserve-3d;
  transform-style: preserve-3d;
  cursor: pointer;
}

.heads,
.tails {
  position: absolute;
  width: 100%;
  height: 100%;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
}

.tails {
  transform: rotateY(180deg);
}

@keyframes spin-tails {
  0% {
    transform: rotateY(0);
  }
  100% {
    transform: rotateY(1980deg);
  }
}
@keyframes spin-heads {
  0% {
    transform: rotateY(0);
  }
  100% {
    transform: rotateY(2160deg);
  }
}

@media (max-width: 640px) {
  #sub_heading {
    font-size: 1rem; /* Hoặc 1rem, tuỳ bạn muốn nhỏ tới mức nào */
  }
}