html {
  height: 100%;
  margin: 0;
  padding: 0;
}

body {
  background: rgb(36, 0, 4);
  background: linear-gradient(0deg, rgb(60, 0, 199) 0%, rgb(77, 101, 147) 35%, rgb(198, 234, 255) 100%);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 1.5em;
  color: Navy;
  text-align: center;
}

h1 {
  font-size: 1.5em;
  margin: .5em 0 .1em 0;
}

#instructions {
  font-size: .7em;
  padding: 0 1em;
  box-sizing: border-box;
}

#game {
  font-family: 'Courier New', Courier, monospace;
}

#game .board-square {
  display: inline-block;
  font-size: 2em;
  background-color: LightSteelBlue;
  border: 2px solid Navy;
  width: 1em;
  height: 1em;
  margin: 0;
  padding: 0;
  text-align: center;
  line-height: 1em;
  box-sizing: border-box;
}

#col-labels {
  cursor: pointer;
}

#col-labels button {
  color: Navy;
  font-size: 1em;
  background-color: LightCyan;
  border: 2px ridge Navy;
  width: 2em;
  height: 2em;
  margin: 0;
  padding: 0;
  text-align: center;
  box-sizing: border-box;
}

.overlay {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  box-sizing: border-box;
  background: rgba(0, 0, 0, 0.7);
  z-index: 2;
}

.dialog-box {
  font-size: .75em;
  position: absolute;
  padding: 2em;
  width: 80%;
  top: 25%;
  left: 10%;
  text-align: center;
  background: LightSteelBlue;
  box-sizing: border-box;
}

.dialog-box p {
  margin: 0 0 1em 0;
  padding: 0;
}

.dialog-box button {
  padding: .8em 1.4em;
  font-size: 1em;
  color: Navy;
  background-color: LightCyan;
  border-color: LightSteelBlue;
}

#game-over {
  font-weight: bold;
  margin-top: 1em;
  padding: .5em;
  box-sizing: border-box;
  background-color: LightSteelBlue;
}

#game-over button {
  padding: .4em .5em;
  font-size: 1em;
  color: Navy;
  background-color: LightCyan;
  border-color: LightSteelBlue;
}