/* ===== ROOT COLOR VARIABLES ===== */
:root {
  --bg-color: #0f0f0f;
  --display-bg: #1e1e1e;
  --btn-bg: #262626;
  --btn-hover: #333;
  --btn-active: #00ffc6;
  --btn-text: #ffffff;
  --accent: #00ffee;
  --border-color: #00ffff2a;
  --shadow-color: rgba(0, 255, 255, 0.3);
  --font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
}

/* ===== THEME: RETRO / ARCADE ===== */
.theme-retro {
  --bg-color: #1a1a1a;
  --display-bg: #0f0f0f;
  --btn-bg: #222;
  --btn-hover: #333;
  --btn-active: #ff00ff;
  --btn-text: #00ff00;
  --accent: #ffcc00;
  --border-color: #ff00ff33;
  --shadow-color: rgba(255, 0, 255, 0.4);
}

/* ===== THEME: MOBILE APP INSPIRED ===== */
.theme-mobile {
  --bg-color: #f5f5f5;
  --display-bg: #ffffff;
  --btn-bg: #e0e0e0;
  --btn-hover: #d5d5d5;
  --btn-active: #007bff;
  --btn-text: #000000;
  --accent: #007bff;
  --border-color: #007bff33;
  --shadow-color: rgba(0, 123, 255, 0.3);
}

/* ===== THEME: CYBERPUNK ===== */
.theme-cyberpunk {
  --bg-color: #0f0c29;
  --display-bg: #302b63;
  --btn-bg: #24243e;
  --btn-hover: #333;
  --btn-active: #00ffff;
  --btn-text: #ffffff;
  --accent: #ff00cc;
  --border-color: #ff00cc33;
  --shadow-color: rgba(255, 0, 204, 0.4);
}

:root,
.theme-retro,
.theme-mobile,
.theme-cyberpunk {
  transition: background-color 0.6s ease, color 0.6s ease;
}

/* ===== GENERAL RESET ===== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: var(--font-family);
  background-color: var(--bg-color);
  color: var(--btn-text);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

/* ===== CALCULATOR CONTAINER ===== */
.calculator-container {
  padding: 1rem;
}

.calculator {
  background: var(--display-bg);
  border-radius: 1.2rem;
  box-shadow: 0 0 25px var(--shadow-color);
  padding: 2rem;
  max-width: 350px;
  width: 100%;
}

/* ===== HEADER ===== */
.calculator-header {
  text-align: center;
  margin-bottom: 1rem;
}

.calculator-header .title {
  color: var(--accent);
  font-size: 1.8rem;
  letter-spacing: 2px;
}

/* ===== DISPLAY ===== */
.display-screen {
  background: var(--btn-bg);
  color: var(--btn-text);
  border-radius: 0.6rem;
  padding: 1rem;
  text-align: right;
  font-size: 2rem;
  margin-bottom: 1.5rem;
  box-shadow: inset 0 0 10px var(--shadow-color);
  word-wrap: break-word;
  min-height: 60px;
}

/* ===== BUTTONS GRID ===== */
.buttons-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.8rem;
}

.button-row {
  display: contents;
}

/* ===== BUTTON STYLES ===== */
.btn {
  background-color: var(--btn-bg);
  color: var(--btn-text);
  border: 1px solid var(--border-color);
  border-radius: 0.6rem;
  font-size: 1.2rem;
  padding: 1rem;
  cursor: pointer;
  transition: 0.3s;
  box-shadow: 0 4px 8px rgba(0, 255, 255, 0.1);
}

.btn:hover {
  background-color: var(--btn-hover);
  box-shadow: 0 0 10px var(--accent);
  transform: scale(1.05);
}

/* Neon pulse on press */
.btn:active,
.btn.active {
  transform: scale(0.95);
  box-shadow: 0 0 20px var(--accent), 0 0 40px var(--accent);
  transition: transform 0.1s, box-shadow 0.1s;
}

/* ===== SPECIAL BUTTONS ===== */
.btn.operator {
  color: var(--accent);
}

.btn.delete,
.btn.action {
  color: #ff4d4d;
}

.btn.equal {
  background-color: var(--accent);
  color: #000;
  font-weight: bold;
}

/* ==== Theme Switching ==== */

.theme-switcher {
  display: flex;
  justify-content: center;
  gap: 0.5rem;
  margin-bottom: 1.2rem;
  flex-wrap: wrap;
}

.theme-btn {
  padding: 0.5rem 1rem;
  background-color: var(--btn-bg);
  border: 1px solid var(--border-color);
  color: var(--btn-text);
  font-weight: bold;
  cursor: pointer;
  border-radius: 0.5rem;
  transition: background-color 0.3s;
}

.theme-btn:hover {
  background-color: var(--btn-hover);
  box-shadow: 0 0 10px var(--accent);
}

.theme-btn:active {
  color: var(--bg-color);
}

.reset-theme {
  background-color: transparent;
  border: 1px dashed var(--accent);
  color: var(--accent);
  font-weight: bold;
}

.reset-theme:hover {
  color: var(--btn-text);
  background-color: var(--btn-hover);
  box-shadow: 0 0 10px var(--accent);
}

/* ===== RESPONSIVE DESIGN ===== */
@media (max-width: 480px) {
  .calculator {
    padding: 1rem;
    border-radius: 0.8rem;
  }

  .calculator-header .title {
    font-size: 1.4rem;
  }

  .display-screen {
    font-size: 1.5rem;
    padding: 0.8rem;
    min-height: 50px;
  }

  .btn {
    padding: 0.8rem;
    font-size: 1rem;
    border-radius: 0.5rem;
  }

  .buttons-grid {
    gap: 0.6rem;
  }
}