style.css

html,
body {
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
}

main {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
}

h1 {
  text-align: center;
}

.square {
  width: 50px;
  height: 50px;
  background: black;
}

#drawing-canvas {
  background: black;
  border: 1px solid black;
  border-radius: 15%;
  border: 5px solid gray;
}

.btn {
  margin: 10px 10px;
  padding: 15px 20px;
  font-size: 15px;
  font-weight: bold;
  border-radius: 15px;
  transition: all 300ms ease-in-out;
}

.btn:hover {
  cursor: pointer;
}

.btn:focus {
  outline: none;
}

.btn:active {
  outline: none;
  border-bottom: none;
}

.green {
  border: none;
  background: limegreen;
  color: white;
  border-bottom: 5px solid green;
}

.red {
  border: none;
  background: rgb(233, 60, 60);
  color: white;
  border-bottom: 5px solid rgb(129, 0, 0);
}

.result {
  margin: 10px 10px;
  padding: 15px 20px;
  width: 200px;
  font-size: 1.3em;
  text-align: center;
  background: gray;
  color: white;
  border-bottom: 5px solid black;
  border-radius: 15px;
  visibility: hidden;
}