body {
  width: 100vw;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-flow: column;
  margin: 0;
  overflow: hidden;
  font-family: "Lato", sans-serif;
  background-color: #000000;
}

.sudoku-container {
  border: 4px solid #1f171f;
  margin: 0 auto;
  position: relative;
  padding: 0 2px;
}
.sudoku-container::before,
.sudoku-container::after {
  position: absolute;
  border-style: solid;
  pointer-events: none;
  content: "";
}
.sudoku-container::before {
  width: 156px;
  border-width: 0 4px;
  border-color: transparent #1f171f transparent #1f171f;
  top: 4px;
  left: 160px;
  bottom: 4px;
}
.sudoku-container::after {
  height: 156px;
  border-width: 4px 0;
  border-color: #1f171f transparent #1f171f transparent;
  left: 4px;
  top: 160px;
  right: 4px;
}

tr:nth-child(1) td:nth-child(3) input,
tr:nth-child(1) td:nth-child(6) input {
  margin: 0 10px 0 0;
}

tr:nth-child(3) input,
tr:nth-child(6) input {
  margin: 0 0 10px 0;
}

.sudoku-container input {
  width: 40px;
  height: 40px;
  text-align: center;
  font-size: 20px;
  padding: 0;
  border: 3px #9e9e9e solid;
  background-color: #c4c4c4;
  color: #eee;
}
.sudoku-container input:focus {
  border-color: #4c9689;
}
.sudoku-container input.highlight {
  background-color: #29b6f6;
  border-color: #29b6f6;
}
.sudoku-container input.disabled {
  cursor: not-allowed;
  background-color: #4c9689;
  border-color: #4c9689;
}
.sudoku-container input.disabled.highlight {
  background-color: #29b6f6;
  border-color: #29b6f6;
}

.sudoku-container .invalid {
  border-color: #e74c3c;
}
.sudoku-container .invalid:focus {
  border-color: #e74c3c;
}

.sudoku-container.valid-matrix {
  border-color: #4c9689;
}

#controls {
  margin: 20px 0;
}

.btn.primary {
  background-color: #4c9689;
  box-shadow: inset 0 -3px #3b746a;
}