/* ============================================================
   VUNA Calculator — Osadolor Benedict Osegie
   ============================================================ */

/* ---------- CSS Variables ---------- */
:root {
  --bg-grad-a:    #1a1a2e;
  --bg-grad-b:    #16213e;
  --card-bg:      rgba(255, 255, 255, 0.97);
  --display-bg:   #0f3460;
  --display-text: #e2e8f0;
  --btn-num-bg:   #f1f5f9;
  --btn-num-fg:   #1e293b;
  --btn-num-hover:#e2e8f0;
  --btn-op-bg:    #3b82f6;
  --btn-op-fg:    #ffffff;
  --btn-op-hover: #2563eb;
  --btn-ac-bg:    #ef4444;
  --btn-ac-fg:    #ffffff;
  --btn-ac-hover: #dc2626;
  --btn-eq-bg:    #10b981;
  --btn-eq-fg:    #ffffff;
  --btn-eq-hover: #059669;
  --header-bg:    rgba(255,255,255,0.08);
  --header-text:  #e2e8f0;
  --radius:       14px;
  --shadow:       0 20px 60px rgba(0, 0, 0, 0.4);
  --transition:   0.15s ease;
}

/* ---------- Dark Mode Overrides ---------- */
body.dark-mode {
  --card-bg:      rgba(15, 23, 42, 0.97);
  --btn-num-bg:   #1e293b;
  --btn-num-fg:   #e2e8f0;
  --btn-num-hover:#334155;
}

/* ---------- Base ---------- */
*,
*::before,
*::after { box-sizing: border-box; }

body {
  background: linear-gradient(135deg, var(--bg-grad-a) 0%, var(--bg-grad-b) 100%);
  min-height: 100vh;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  padding: 24px 0 48px;
  transition: background var(--transition);
}

/* ---------- Theme Toggle ---------- */
.theme-toggle-btn {
  position: fixed;
  top: 16px;
  right: 16px;
  background: rgba(255,255,255,0.12);
  border: 1px solid rgba(255,255,255,0.2);
  color: #fff;
  border-radius: 50%;
  width: 44px;
  height: 44px;
  font-size: 1.2rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background var(--transition), transform var(--transition);
  z-index: 100;
}
.theme-toggle-btn:hover {
  background: rgba(255,255,255,0.22);
  transform: scale(1.1);
}

/* ---------- Header ---------- */
.calc-header {
  background: var(--header-bg);
  border: 1px solid rgba(255,255,255,0.12);
  border-radius: var(--radius);
  padding: 16px 20px 12px;
  margin-bottom: 12px;
  text-align: center;
}
.calc-title {
  color: var(--header-text);
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: 2px;
  margin: 0 0 4px;
}
.calc-subtitle {
  color: rgba(226, 232, 240, 0.6);
  font-size: 0.8rem;
  margin: 0;
  letter-spacing: 0.5px;
}

/* ---------- Keyboard hint ---------- */
.kb-hint {
  text-align: center;
  font-size: 0.75rem;
  color: rgba(226, 232, 240, 0.45);
  margin-bottom: 10px;
  min-height: 18px;
  transition: color 0.3s;
}
.kb-hint.active {
  color: #10b981;
}

/* ---------- Card ---------- */
.calculator-card {
  background: var(--card-bg);
  border: none;
  border-radius: 20px;
  box-shadow: var(--shadow);
  overflow: hidden;
  transition: background var(--transition);
}

/* ---------- Display ---------- */
.calc-display {
  width: 100%;
  background: var(--display-bg);
  border: none;
  border-radius: var(--radius);
  color: var(--display-text);
  font-size: 2rem;
  font-weight: 500;
  text-align: right;
  padding: 18px 20px;
  margin-bottom: 18px;
  min-height: 68px;
  letter-spacing: 1px;
  box-shadow: inset 0 2px 10px rgba(0,0,0,0.3);
}
.calc-display:disabled {
  opacity: 1;
  cursor: default;
}
/* flash effect on keyboard press */
.calc-display.flash {
  background: #1d4ed8;
  transition: background 0.05s;
}

/* ---------- Button Grid ---------- */
.btn-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

/* Span helpers */
.col-span-2 { grid-column: span 2; }
.row-span-2 { grid-row: span 2; }

/* ---------- Buttons — base ---------- */
.btn-grid .btn {
  border: none;
  border-radius: 12px;
  font-size: 1.3rem;
  font-weight: 600;
  height: 62px;
  cursor: pointer;
  transition: transform var(--transition), box-shadow var(--transition), background var(--transition);
  box-shadow: 0 4px 12px rgba(0,0,0,0.12);
  display: flex;
  align-items: center;
  justify-content: center;
}
.btn-grid .btn:active,
.btn-grid .btn.pressed {
  transform: scale(0.93);
  box-shadow: 0 2px 6px rgba(0,0,0,0.2);
}

/* Number buttons */
.btn-number {
  background: var(--btn-num-bg);
  color:      var(--btn-num-fg);
}
.btn-number:hover {
  background: var(--btn-num-hover);
  color:      var(--btn-num-fg);
}

/* Operator buttons */
.btn-operator {
  background: var(--btn-op-bg);
  color:      var(--btn-op-fg);
}
.btn-operator:hover {
  background: var(--btn-op-hover);
  color:      var(--btn-op-fg);
}

/* AC / ← buttons */
.btn-action {
  background: var(--btn-ac-bg);
  color:      var(--btn-ac-fg);
}
.btn-action:hover {
  background: var(--btn-ac-hover);
  color:      var(--btn-ac-fg);
}

/* Equals button */
.btn-equals {
  background: var(--btn-eq-bg);
  color:      var(--btn-eq-fg);
  font-size: 1.6rem;
}
.btn-equals:hover {
  background: var(--btn-eq-hover);
  color:      var(--btn-eq-fg);
}