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

body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(135deg, #1a1a40, #2c2c54);
  color: #f4f4f4;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
  padding: 40px 20px;
}

h1 {
  font-size: 3rem;
  margin-bottom: 10px;
  color: #00ffe5;
  text-shadow: 0 0 10px #00ffe5a1;
}

h2 {
  font-size: 1.2rem;
  color: #cccccc;
  margin-bottom: 40px;
}

.outer-circle {
  position: relative;
  width: 90vw;
  height: 90vw;
  max-width: 500px;
  max-height: 500px;
  border-radius: 50%;
  background: black;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  grid-template-rows: repeat(2, 1fr);
  gap: 20px;
  padding: 30px;
  box-shadow: 0 0 40px rgba(0, 0, 0, 0.5);
}

.btn {
  width: 100%;
  height: 100%;
  border: none;
  outline: none;
  cursor: pointer;
  box-shadow: inset 0 0 0 4px rgba(255, 255, 255, 0.2);
  transition: filter 0.2s ease, box-shadow 0.2s ease;
  padding: 0;
}

.green{
    border-radius: 100% 5% 5% 5%;
}
.red{
    border-radius: 5% 100% 5% 5%;
}
.blue{
    border-radius: 5% 5% 100% 5%;
}
.yellow{
    border-radius: 5% 5% 5% 100%;
}

.btn:hover {
  filter: brightness(1.1);
  box-shadow: inset 0 0 0 4px rgba(255, 255, 255, 0.3);
}

.green {
  background: linear-gradient(145deg, #00c851, #007e33);
}

.red {
  background: linear-gradient(145deg, #ff4444, #cc0000);
}

.yellow {
  background: linear-gradient(145deg, #ffbb33, #ff8800);
}

.blue {
  background: linear-gradient(145deg, #33b5e5, #0099cc);
}

.flash {
  background: #ffffff !important;
  box-shadow: 0 0 30px #ffffff;
  transition: background 0.15s ease, box-shadow 0.15s ease;
}

.center {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 180px;
  height: 180px;
  background-color: black;
  color: white;
  transform: translate(-50%, -50%);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 2;
  font-weight: bold;
  font-size: 1.2rem;
}

@media (max-width: 500px) {
  .btn-container {
    grid-template-columns: repeat(2, 120px);
    grid-template-rows: repeat(2, 120px);
    gap: 16px;
  }

  .btn {
    width: 120px;
    height: 120px;
  }

  h1 {
    font-size: 2.2rem;
  }

  h2 {
    font-size: 1rem;
  }
  .outer-circle {
    width: 95vw;
    height: 95vw;
    padding: 20px;
    gap: 10px;
  }

  .center {
    width: 80px;
    height: 80px;
    font-size: 1rem;
  }

}