#container {
  display: flex;
  justify-content: center;
}

p, span, input, button {
  margin-top: 0;
  font-size: 2.5vw
}

button {
  margin: 2vw 0;
}

#grid-container {
  width: 54vw;
  height: 54vw;
  margin-bottom: 5vw
}

#grid {
  width: 100%;
  height: 100%;
  border: 2px solid;
  border-collapse: collapse;
}

#grid table {
  table-layout: fixed;
  border: 1px solid;
  border-collapse: collapse;
  margin: -1px;
  width: 18vw;
  height: 18vw;
}

#grid table td {
  border: 1px solid;
  overflow: hidden;
}

.box {
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: center;
  font-size: 4vw;
}

.flash-red { animation: flash-red 3s; }

@keyframes flash-red {
  0%   { border-color: red; }
  50%  { border-color: #500; }
  100% { border-color: black; }
}