:root {
  --dark-color: #333;
  --light-color: #fff;
  --mark-size: calc(100px * 0.9);
}

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

/* utility class */
.hide {
  visibility: hidden;
}

body {
  background-color: #5a3e79;
  font-family: "Roboto", sans-serif;
  color: var(--dark-color);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
}

.game-start,
.game-over {
  position: absolute;
  width: 400px;
  height: 400px;
  background-color: var(--light-color);
  border-radius: 10px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2rem;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.2);
}

.game-start__title,
.game-over__text {
  font-size: 3rem;
  font-weight: 700;
}

.game-start__button,
.game-over__button {
  padding: 1rem 2rem;
  border: none;
  border-radius: 5px;
  background-color: var(--dark-color);
  color: var(--light-color);
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.2);
  font-size: 1.25rem;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.3s ease-in-out;
}

.game-start__button:hover,
.game-over__button:hover {
  transform: scale(1.1);
}

.game-start__button:active,
.game-over__button:active {
  transform: scale(0.9);
}

.gameboard-container {
  position: absolute;
  width: 400px;
  height: 400px;
  background-color: var(--light-color);
  border-radius: 10px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.2);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.gameboard {
  background-color: var(--light-color);
  width: 300px;
  height: 300px;
  display: grid;
  grid-template-columns: repeat(3, 100px);
  grid-template-rows: repeat(3, 100px);
}

.gameboard__cell {
  background-color: var(--light-color);
  display: flex;
  align-items: center;
  justify-content: center;
  border: 2px solid var(--dark-color);
  cursor: pointer;
  position: relative;
}

.gameboard__cell:nth-child(3n + 1) {
  border-left: none;
}

.gameboard__cell:nth-child(3n + 3) {
  border-right: none;
}

.gameboard__cell:nth-child(-n + 3) {
  border-top: none;
}

.gameboard__cell:nth-child(n + 7) {
  border-bottom: none;
}

.circle {
  width: var(--mark-size);
  height: var(--mark-size);
  border-radius: 50%;
  background-color: transparent;
  border: calc(var(--mark-size) * 0.2) solid var(--dark-color);
}

.cross::before,
.cross::after {
  content: "";
  position: absolute;
  background-color: var(--dark-color);
  width: calc(var(--mark-size) * 0.2);
  height: var(--mark-size);
}

.cross::before {
  transform: translate(-50%, -50%) rotate(45deg);
}

.cross::after {
  transform: translate(-50%, -50%) rotate(-45deg);
}