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

body {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  font-family: sans-serif;
  background: linear-gradient(135deg, #1e1e1e 0%, #2d2d2d 100%);
  padding: 20px;
}

.container {
  width: 400px;
  max-width: 100%;
  background-color: #000000;
  padding: 40px;
  border-radius: 18px;
  box-shadow:
    0 20px 60px rgba(0, 0, 0, 0.5),
    0 0 100px rgba(0, 0, 0, 0.3);
}

.container > input {
  border-radius: 12px;
  margin-bottom: 20px;
  background: rgba(255, 255, 255, 0.05);
  outline: none;
  border: none;
  color: #ffffff;
  font-size: 40px;
  padding: 30px 35px;
  text-align: right;
  width: 100%;
  border: 1px solid rgba(255, 255, 255, 0.1);
  text-shadow:
    0 0 10px rgba(255, 255, 255, 0.3),
    0 0 20px rgba(255, 255, 255, 0.2),
    0 2px 4px rgba(0, 0, 0, 0.5);
}

.container > input::placeholder {
  color: #ffffff;
}

.all-btn {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
  justify-items: center;
  align-items: center;
}

.all-btn > div {
  display: contents;
}

button {
  background: #333333;
  color: #ffffff;
  font-weight: bolder;
  width: 65px;
  height: 65px;
  border-radius: 50%;
  font-size: 18px;
  border: none;
  outline: none;
  box-shadow: 0 0 18px rgba(255, 255, 255, 0.3);
  transition: all 0.2s ease;
}

button:hover {
  cursor: pointer;
  font-weight: bolder;
  transform: translateY(-2px);
  box-shadow: 0 5px 20px rgba(255, 255, 255, 0.4);
}

button:focus,
button:active {
  font-weight: bolder;
  outline: none;
  transform: scale(0.95);
  transition: transform 0.1s;
}

.operator {
  background: #ff9500 !important;
  color: #000000;
  font-size: 20px;
  font-weight: bolder;
  box-shadow:
    0 0 20px rgba(255, 149, 0, 0.2),
    0 0 40px rgba(255, 149, 0, 0.3),
    0 4px 15px rgba(0, 0, 0, 0.3);
}

.operator:hover {
  background: #ffad33 !important;
  box-shadow:
    0 0 20px rgba(255, 149, 0, 0.2),
    0 0 40px rgba(255, 149, 0, 0.3),
    0 4px 15px rgba(0, 0, 0, 0.3);
}

.function {
  font-weight: 750;
  background: #4b4848 !important;
}

.function:hover {
  background: #585656 !important;
}

@media (min-width: 768px) and (max-width: 1024px) {
  .container {
    width: 420px;
    padding: 35px;
  }

  button {
    width: 60px;
    height: 60px;
    font-size: 17px;
  }

  .container > input {
    font-size: 35px;
    padding: 25px 30px;
  }

  .all-btn {
    gap: 12px;
  }
}

@media (min-width: 480px) and (max-width: 767px) {
  .container {
    width: 100%;
    max-width: 400px;
    padding: 30px;
  }

  button {
    width: 55px;
    height: 55px;
    font-size: 16px;
  }

  .container > input {
    font-size: 32px;
    padding: 22px 28px;
  }

  .all-btn {
    gap: 12px;
  }
}

@media (min-width: 375px) and (max-width: 479px) {
  .container {
    width: 100%;
    padding: 25px;
  }

  button {
    width: 50px;
    height: 50px;
    font-size: 15px;
  }

  .container > input {
    font-size: 28px;
    padding: 20px 25px;
  }

  .all-btn {
    gap: 10px;
  }

  .operator {
    font-size: 18px;
  }
}

@media (min-width: 320px) and (max-width: 374px) {
  body {
    padding: 15px;
  }

  .container {
    width: 100%;
    padding: 20px;
  }

  button {
    width: 45px;
    height: 45px;
    font-size: 14px;
  }

  .container > input {
    font-size: 24px;
    padding: 18px 20px;
    margin-bottom: 15px;
  }

  .all-btn {
    gap: 8px;
  }

  .operator {
    font-size: 16px;
  }
}

@media (max-width: 319px) {
  body {
    padding: 10px;
  }

  .container {
    width: 100%;
    padding: 15px;
  }

  button {
    width: 40px;
    height: 40px;
    font-size: 12px;
  }

  .container > input {
    font-size: 20px;
    padding: 15px 18px;
    margin-bottom: 12px;
  }

  .all-btn {
    gap: 6px;
  }

  .operator {
    font-size: 14px;
  }
}

@media (min-width: 1920px) {
  .container {
    width: 500px;
    padding: 50px;
  }

  button {
    width: 80px;
    height: 80px;
    font-size: 22px;
  }

  .container > input {
    font-size: 50px;
    padding: 35px 40px;
  }

  .all-btn {
    gap: 18px;
  }

  .operator {
    font-size: 24px;
  }
}