* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: 'Poppins', 'Segoe UI', sans-serif;
  transition: all 0.3s ease;
}

body {
  background: linear-gradient(135deg, #f8f9fb, #e0e5ec);
  color: #000;
  min-height: 100vh;
}

/* 🌗 دکمه تغییر تم */
.theme-toggle-container {
  display: flex;
  justify-content: right;
  margin: 20px 30px;
}

#theme-toggle {
  padding: 12px 20px;
  font-size: 18px;
  font-weight: 600;
  border: none;
  border-radius: 50px;
  background: linear-gradient(135deg, #333, #555);
  color: #fff;
  cursor: pointer;
  box-shadow: 0 4px 15px rgba(0,0,0,0.3);
  transition: all 0.3s ease-in-out;
}

#theme-toggle:hover {
  transform: scale(1.05);
  background: linear-gradient(135deg, #444, #666);
}

.calculator {
  background: #f0f0f3;
  padding: 25px;
  max-width: 400px;
  margin: 40px auto;
  border-radius: 20px;
  box-shadow: 8px 8px 16px #d1d9e6,
              -8px -8px 16px #ffffff;
}

#result {
  width: 100%;
  padding: 15px;
  font-size: 26px;
  border: none;
  border-radius: 12px;
  background: #e9e9ec;
  box-shadow: inset 3px 3px 6px #d1d9e6,
              inset -3px -3px 6px #ffffff;
  margin-bottom: 15px;
  color: #222;
  outline: none;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-gap: 15px;
}

button {
  padding: 18px;
  font-size: 22px;
  border: none;
  border-radius: 12px;
  background: #f0f0f3;
  box-shadow: 6px 6px 12px #d1d9e6,
              -6px -6px 12px #ffffff;
  cursor: pointer;
  transition: all 0.2s ease-in-out;
  color: #333;
  font-weight: 500;
}

button:hover {
  transform: translateY(-3px);
  box-shadow: 4px 4px 10px #c8d0e7,
              -4px -4px 10px #ffffff;
}

button:active {
  box-shadow: inset 4px 4px 10px #c8d0e7,
              inset -4px -4px 10px #ffffff;
  transform: scale(0.97);
}

.clear {
  background: linear-gradient(135deg, #ff5f6d, #ff2a44);
  color: #fff;
}

.operator {
  background: linear-gradient(135deg, #0074d9, #005fa3);
  color: #fff;
}

.equal {
  background: linear-gradient(135deg, #00c853, #009624);
  color: #fff;
  grid-row: span 2;
}


/* 🌙 تم تاریک مدرن (گلس‌مورفیک) */
body.dark {
  background: radial-gradient(circle at top left, #000, #121212);
  color: #f5f5f5;
}

body.dark .calculator {
  background: rgba(30, 30, 30, 0.6);
  border: 1px solid rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(12px);
  box-shadow: 0 10px 25px rgba(0,0,0,0.6);
}

body.dark #result {
  background: rgba(40, 40, 40, 0.6);
  color: orange;
  box-shadow: inset 0 2px 8px rgba(0,0,0,0.7);
}

body.dark button {
  background: rgba(35, 35, 35, 0.7);
  color: #f1f1f1;
  box-shadow: 0 4px 12px rgba(0,0,0,0.6);
  border: 1px solid rgba(255, 255, 255, 0.05);
}

body.dark button:hover {
  background: rgba(60, 60, 60, 0.8);
  transform: translateY(-2px);
}

body.dark .clear {
  background: linear-gradient(135deg, #ff3b3b, #b30000);
}

body.dark .operator {
  background: linear-gradient(135deg, #1565c0, #0d47a1);
}

body.dark .equal {
  background: linear-gradient(135deg, #00e676, #00c853);
}

body.dark #theme-toggle {
  background: linear-gradient(135deg, #f2f2f2, #ccc);
  color: #000;
  box-shadow: 0 4px 12px rgba(255, 255, 255, 0.589);
}