style.css

:root {
  --color-light-1: #fff;
  --color-light-2: #e8e8e8;
  --color-light-3: #d8ebe4;
  --color-dark: #6b011f;
  --color-button: #0033cc;
}

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

body {
  background-color: var(--color-light-2);
}

h2 {
  margin: 1em;
  font-size: 2rem;
  text-align: center;
  color: #693c72;
}

.container {
  height: 100vh;
  width: 100vw;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

.row {
  display: flex;
  justify-content: center;
  align-items: center;
}

.column {
  width: 60px;
  height: 60px;
  cursor: pointer;
  text-align: center;
  font-size: 2.9em;
}

.box1,
.box2 {
  border-right: 3px solid var(--color-dark);
  border-bottom: 3px solid var(--color-dark);
}

.box4,
.box5,
.box8,
.box7 {
  border-right: 3px solid var(--color-dark);
}

.box3,
.box4,
.box5,
.box6 {
  border-bottom: 3px solid var(--color-dark);
}

.winner {
  margin: 1rem;
  font-size: 1.5rem;
  color: var(--color-button);
}

.restart {
  width: 5rem;
  height: 2rem;
  background-color: #007580;
  font-weight: 600;
  font-size: 1rem;
  border-radius: 0.3rem;
  border: none;
  outline: none;
  color: var(--color-light-3);
  cursor: pointer;
}