/* Reset & Core Setup */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

:root {
  /* Common transitions */
  --transition-speed: 0.25s;
  --transition-bezier: cubic-bezier(0.4, 0, 0.2, 1);
  --accent-color: #3B82F6;
  --accent-color-hover: #2563EB;
}

/* Light Theme Variables */
body.light {
  --bg-color: #E8ECEF;
  --text-primary: #1A1A1A;
  --text-secondary: #70757A;
  --card-bg: linear-gradient(135deg, rgba(245, 247, 250, 0.8) 0%, rgba(255, 255, 255, 0.8) 100%);
  --card-border: rgba(255, 255, 255, 0.6);
  --card-shadow: 0 20px 50px rgba(74, 127, 193, 0.2), 0 1px 3px rgba(0, 0, 0, 0.05);
  
  --btn-num-bg: #F0F2F5;
  --btn-num-text: #1A1A1A;
  --btn-num-hover: #E4E7EB;
  
  --btn-op-bg: #E8EBEF;
  --btn-op-text: #1A1A1A;
  --btn-op-hover: #DDE2E7;
  
  --btn-util-bg: #E8EBEF;
  --btn-util-text: #8B8F98;
  --btn-util-hover: #DDE2E7;
  
  --btn-sci-bg: rgba(232, 235, 239, 0.6);
  --btn-sci-text: #606770;
  --btn-sci-hover: rgba(221, 226, 231, 0.8);
  
  --toggle-btn-bg: rgba(255, 255, 255, 0.8);
  --toggle-btn-border: rgba(0, 0, 0, 0.05);
  --toggle-btn-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
  --toggle-icon-color: #4A5568;
}

/* Dark Theme Variables */
body.dark {
  --bg-color: #0A0B0E;
  --text-primary: #FFFFFF;
  --text-secondary: #8B8F98;
  --card-bg: linear-gradient(135deg, rgba(21, 23, 28, 0.9) 0%, rgba(13, 14, 18, 0.95) 100%);
  --card-border: rgba(255, 255, 255, 0.06);
  --card-shadow: 0 25px 60px rgba(0, 0, 0, 0.55), inset 0 1px 2px rgba(255, 255, 255, 0.05);
  
  --btn-num-bg: #23262E;
  --btn-num-text: #FFFFFF;
  --btn-num-hover: #2E323D;
  
  --btn-op-bg: #2C2F38;
  --btn-op-text: #FFFFFF;
  --btn-op-hover: #373B46;
  
  --btn-util-bg: #23262E;
  --btn-util-text: #8B8F98;
  --btn-util-hover: #2E323D;
  
  --btn-sci-bg: rgba(35, 38, 46, 0.6);
  --btn-sci-text: #B2B6C1;
  --btn-sci-hover: rgba(46, 50, 61, 0.8);
  
  --toggle-btn-bg: rgba(35, 38, 46, 0.8);
  --toggle-btn-border: rgba(255, 255, 255, 0.05);
  --toggle-btn-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  --toggle-icon-color: #E2E8F0;
}

body {
  font-family: 'Outfit', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-primary);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow-x: hidden;
  transition: background-color var(--transition-speed) ease;
}

/* App Container and Background Glow */
.app-container {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  width: 100%;
  padding: 40px 20px;
}

.ambient-glow {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 480px;
  height: 480px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(59, 130, 246, 0.45) 0%, rgba(59, 130, 246, 0) 70%);
  filter: blur(80px);
  z-index: 1;
  pointer-events: none;
  transition: background var(--transition-speed) ease, transform 0.5s ease;
}

body.dark .ambient-glow {
  background: radial-gradient(circle, rgba(59, 130, 246, 0.55) 0%, rgba(59, 130, 246, 0) 70%);
}

/* Calculator Card Styling */
.calculator-card {
  position: relative;
  z-index: 2;
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 32px;
  box-shadow: var(--card-shadow);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  padding: 24px;
  width: 340px;
  min-height: 600px;
  display: flex;
  flex-direction: column;
  gap: 20px;
  overflow: hidden;
  transition: width var(--transition-speed) var(--transition-bezier),
              background var(--transition-speed) ease,
              border-color var(--transition-speed) ease,
              box-shadow var(--transition-speed) ease;
}

.calculator-card.open {
  width: 568px;
}

/* Display Area Styling */
.display-area {
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  height: 140px;
  padding: 10px 8px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
  margin-bottom: 4px;
  text-align: right;
  position: relative;
}

.mode-badge {
  position: absolute;
  top: 4px;
  left: 8px;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  color: var(--accent-color);
  background: rgba(59, 130, 246, 0.1);
  padding: 2px 6px;
  border-radius: 6px;
  letter-spacing: 0.5px;
  pointer-events: none;
}

.expression-line {
  font-size: 16px;
  font-weight: 400;
  color: var(--text-secondary);
  word-break: break-all;
  max-height: 48px;
  overflow-y: auto;
  line-height: 1.3;
  margin-bottom: 6px;
  width: 100%;
}

.result-line {
  font-size: 40px;
  font-weight: 600;
  color: var(--text-primary);
  word-break: break-all;
  line-height: 1.1;
  width: 100%;
}

/* Card Body & Panel Layouts */
.card-body {
  display: flex;
  flex-direction: row;
  width: 100%;
  overflow: hidden;
}

/* Scientific Panel (Left Drawer) */
.scientific-panel {
  width: 0;
  opacity: 0;
  visibility: hidden;
  overflow: hidden;
  transition: width var(--transition-speed) var(--transition-bezier),
              opacity var(--transition-speed) var(--transition-bezier),
              margin-right var(--transition-speed) var(--transition-bezier);
  margin-right: 0;
}

.calculator-card.open .scientific-panel {
  width: 216px;
  opacity: 1;
  visibility: visible;
  margin-right: 12px;
}

.scientific-grid {
  display: grid;
  grid-template-columns: repeat(3, 64px);
  grid-template-rows: repeat(6, 64px);
  gap: 12px;
  width: 216px;
}

/* Main Button Grid */
.button-grid {
  display: grid;
  grid-template-columns: repeat(4, 64px);
  grid-template-rows: repeat(6, 64px);
  gap: 12px;
  width: 292px;
}

/* Base Button Styling */
.btn {
  width: 64px;
  height: 64px;
  border-radius: 50%;
  border: none;
  font-family: inherit;
  font-size: 20px;
  font-weight: 500;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  user-select: none;
  outline: none;
  transition: background-color 0.15s ease, color 0.15s ease, transform 0.15s ease, box-shadow 0.15s ease;
}

/* Focus States for Accessibility */
.btn:focus-visible {
  box-shadow: 0 0 0 3px var(--accent-color);
}

/* Tactile Active Animation */
.btn:active {
  transform: scale(0.92);
  opacity: 0.85;
}

/* Button Subtypes */
.number-btn {
  background-color: var(--btn-num-bg);
  color: var(--btn-num-text);
}
.number-btn:hover {
  background-color: var(--btn-num-hover);
}

.operator-btn {
  background-color: var(--btn-op-bg);
  color: var(--btn-op-text);
}
.operator-btn:hover {
  background-color: var(--btn-op-hover);
}

.utility-btn {
  background-color: var(--btn-util-bg);
  color: var(--btn-util-text);
}
.utility-btn:hover {
  background-color: var(--btn-util-hover);
}

.scientific-btn {
  background-color: var(--btn-sci-bg);
  color: var(--btn-sci-text);
  font-size: 18px;
}
.scientific-btn:hover {
  background-color: var(--btn-sci-hover);
}

/* Active Operator Key Highlight */
.operator-btn.active {
  background-color: var(--accent-color) !important;
  color: #FFFFFF !important;
  box-shadow: 0 0 12px rgba(59, 130, 246, 0.4);
}

/* Specific Equals Button pill */
.equals-btn {
  grid-column: 4;
  grid-row: 5 / 7;
  width: 64px;
  height: 140px;
  border-radius: 32px;
  background-color: var(--accent-color);
  color: #FFFFFF;
  font-size: 24px;
  font-weight: 600;
  box-shadow: 0 8px 20px rgba(59, 130, 246, 0.3);
}
.equals-btn:hover {
  background-color: var(--accent-color-hover);
  box-shadow: 0 8px 24px rgba(59, 130, 246, 0.45);
}

/* Deg/Rad Scientific Switch Label */
.deg-rad-btn {
  font-size: 13px;
  font-weight: 600;
  display: flex;
  gap: 1px;
  align-items: center;
  justify-content: center;
}
.deg-rad-btn .slash {
  opacity: 0.4;
  font-weight: 400;
}
.deg-rad-btn span.active {
  color: var(--accent-color);
}

/* Inline Deg/Rad toggle styling (top row of main grid) */
.inline-deg-rad-btn {
  font-size: 15px;
  text-transform: uppercase;
}

/* Theme Toggle Button */
.theme-toggle-btn {
  position: fixed;
  top: 24px;
  right: 24px;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  border: 1px solid var(--toggle-btn-border);
  background: var(--toggle-btn-bg);
  box-shadow: var(--toggle-btn-shadow);
  color: var(--toggle-icon-color);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  z-index: 100;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1),
              background-color var(--transition-speed) ease,
              color var(--transition-speed) ease,
              border-color var(--transition-speed) ease;
}

.theme-toggle-btn:hover {
  transform: rotate(45deg) scale(1.05);
}

.theme-toggle-btn svg {
  width: 20px;
  height: 20px;
  position: absolute;
  transition: transform 0.5s var(--transition-bezier), opacity 0.3s ease;
}

body.dark .sun-icon {
  transform: scale(0) rotate(-90deg);
  opacity: 0;
}
body.dark .moon-icon {
  transform: scale(1) rotate(0);
  opacity: 1;
}

body.light .sun-icon {
  transform: scale(1) rotate(0);
  opacity: 1;
}
body.light .moon-icon {
  transform: scale(0) rotate(90deg);
  opacity: 0;
}

/* Responsive Scaling for Mobile Screens */
@media (max-width: 600px) {
  /* On small screens, instead of expanding horizontally, 
     we scale the calculator card down slightly, or overlay the drawer.
     But expanding horizontally works if we scale down! */
  .app-container {
    transform-origin: center center;
    padding: 20px 10px;
  }
  
  .calculator-card.open {
    /* Limit the open card to display cleanly on narrow screens */
    width: 340px; 
    /* Let's stack the scientific panel on top or make it an overlay! */
  }

  .calculator-card.open .scientific-panel {
    position: absolute;
    top: 172px; /* Place below display area */
    left: 24px;
    width: 292px; /* Matches main grid width */
    height: 444px;
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: 20px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.25);
    z-index: 10;
    margin-right: 0;
    backdrop-filter: blur(30px);
    -webkit-backdrop-filter: blur(30px);
  }

  .calculator-card.open .scientific-grid {
    grid-template-columns: repeat(4, 64px); /* Make it 4 cols on mobile overlay! */
    grid-template-rows: repeat(5, 64px);
    width: 100%;
    padding: 10px;
  }
}