/* ── Reset & Base ─────────────────────────────────────── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg-deep:       #0a0f1e;
  --bg-mid:        #111827;
  --bg-card:       #161d2e;
  --glass:         rgba(255,255,255,0.06);
  --glass-hover:   rgba(255,255,255,0.12);
  --glass-active:  rgba(255,255,255,0.18);
  --border:        rgba(255,255,255,0.08);

  --accent-blue:   #3b82f6;
  --accent-teal:   #06b6d4;
  --accent-green:  #10b981;
  --accent-amber:  #f59e0b;
  --accent-rose:   #f43f5e;

  --text-primary:  #f1f5f9;
  --text-muted:    rgba(255,255,255,0.45);
  --text-dim:      rgba(255,255,255,0.25);

  --radius-sm:     10px;
  --radius-md:     16px;
  --radius-lg:     24px;

  --font-display:  'DM Mono', monospace;
  --font-ui:       'DM Sans', sans-serif;
  --transition:    0.18s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ── Body & Layout ────────────────────────────────────── */
body {
  font-family: var(--font-ui);
  background-color: var(--bg-deep);
  background-image:
    radial-gradient(ellipse 80% 50% at 20% 10%, rgba(59,130,246,0.12) 0%, transparent 60%),
    radial-gradient(ellipse 60% 40% at 80% 90%, rgba(6,182,212,0.10) 0%, transparent 55%),
    radial-gradient(ellipse 50% 60% at 50% 50%, rgba(16,185,129,0.04) 0%, transparent 70%);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 20px;
  overflow-x: hidden;
}

.app-wrapper {
  display: flex;
  align-items: flex-start;
  gap: 24px;
  max-width: 1100px;
  width: 100%;
  justify-content: center;
}

/* ── Calculator Grid ──────────────────────────────────── */
.calculator-grid {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 20px;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  box-shadow:
    0 0 0 1px rgba(255,255,255,0.04) inset,
    0 24px 60px rgba(0,0,0,0.5),
    0 0 80px rgba(59,130,246,0.06);
  width: min(95vw, 380px);
}

.sci-grid {
  grid-template-columns: repeat(7, 1fr);
  width: min(95vw, 720px);
}

/* ── Output Display ───────────────────────────────────── */
.output {
  grid-column: 1 / -1;
  background: rgba(0,0,0,0.4);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 14px 18px 16px;
  min-height: 110px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 6px;
  position: relative;
  overflow: hidden;
}

.output::before {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba(59,130,246,0.04), transparent 60%);
  pointer-events: none;
}

.output-top-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.previous-operand {
  font-family: var(--font-display);
  font-size: 0.85rem;
  color: var(--text-muted);
  min-height: 20px;
  text-align: right;
  letter-spacing: 0.02em;
}

.current-operand {
  font-family: var(--font-display);
  font-size: 2.2rem;
  font-weight: 400;
  color: var(--text-primary);
  background: transparent;
  border: none;
  outline: none;
  text-align: right;
  width: 100%;
  letter-spacing: -0.02em;
  caret-color: transparent;
  cursor: default;
}

@keyframes blink-once {
  0%   { opacity: 0.6; }
  100% { opacity: 1; }
}
.current-operand.blink {
  animation: blink-once 0.12s ease-out forwards;
}

/* ── Toggle Button ────────────────────────────────────── */
.toggle-btn {
  display: flex;
  align-items: center;
  gap: 5px;
  background: rgba(59,130,246,0.15);
  border: 1px solid rgba(59,130,246,0.3);
  border-radius: 8px;
  padding: 4px 10px 4px 6px;
  cursor: pointer;
  transition: var(--transition);
  color: var(--accent-blue);
}
.toggle-btn:hover {
  background: rgba(59,130,246,0.25);
}
.toggle-btn img {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  object-fit: cover;
}
.toggle-label {
  font-family: var(--font-display);
  font-size: 0.65rem;
  font-weight: 500;
  letter-spacing: 0.1em;
}

/* ── Mode Badge ───────────────────────────────────────── */
.mode-badge {
  font-family: var(--font-display);
  font-size: 0.65rem;
  font-weight: 500;
  letter-spacing: 0.12em;
  padding: 3px 9px;
  border-radius: 6px;
  border: 1px solid;
}
.mode-badge.deg {
  color: var(--accent-amber);
  border-color: rgba(245,158,11,0.35);
  background: rgba(245,158,11,0.1);
}
.mode-badge.rad {
  color: var(--accent-teal);
  border-color: rgba(6,182,212,0.35);
  background: rgba(6,182,212,0.1);
}

/* ── Buttons Base ─────────────────────────────────────── */
.btn {
  font-family: var(--font-display);
  font-size: 1.05rem;
  color: var(--text-primary);
  background: var(--glass);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  min-height: 58px;
  cursor: pointer;
  transition: var(--transition);
  position: relative;
  overflow: hidden;
  letter-spacing: 0.01em;
  display: flex;
  align-items: center;
  justify-content: center;
}
.btn:hover {
  background: var(--glass-hover);
  transform: translateY(-1px);
  border-color: rgba(255,255,255,0.14);
  box-shadow: 0 4px 12px rgba(0,0,0,0.3);
}
.btn:active {
  background: var(--glass-active);
  transform: translateY(0);
  box-shadow: none;
}
.btn.keyboard-active {
  background: rgba(255,255,255,0.22);
  transform: scale(0.93);
  box-shadow: 0 0 0 2px var(--accent-blue);
}

/* ── Button Variants ──────────────────────────────────── */
.btn-operator {
  color: var(--accent-teal);
  background: rgba(6,182,212,0.08);
  border-color: rgba(6,182,212,0.18);
  font-size: 1.2rem;
}
.btn-operator:hover {
  background: rgba(6,182,212,0.18);
  border-color: rgba(6,182,212,0.35);
}

.btn-equals {
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-teal));
  border: none;
  color: white;
  font-size: 1.4rem;
  font-weight: 500;
  box-shadow: 0 4px 20px rgba(59,130,246,0.35);
}
.btn-equals:hover {
  background: linear-gradient(135deg, #60a5fa, #22d3ee);
  box-shadow: 0 6px 25px rgba(59,130,246,0.5);
  transform: translateY(-2px);
}
.btn-equals:active {
  transform: translateY(0);
}

.btn-utility {
  color: var(--accent-rose);
  background: rgba(244,63,94,0.08);
  border-color: rgba(244,63,94,0.18);
  font-size: 0.9rem;
  letter-spacing: 0.06em;
}
.btn-utility:hover {
  background: rgba(244,63,94,0.18);
  border-color: rgba(244,63,94,0.35);
}

.btn-fn {
  color: #c4b5fd;
  background: rgba(139,92,246,0.08);
  border-color: rgba(139,92,246,0.18);
  font-size: 0.9rem;
}
.btn-fn:hover {
  background: rgba(139,92,246,0.18);
  border-color: rgba(139,92,246,0.3);
}

.btn-trig {
  color: var(--accent-green);
  background: rgba(16,185,129,0.08);
  border-color: rgba(16,185,129,0.18);
  font-size: 0.9rem;
}
.btn-trig:hover {
  background: rgba(16,185,129,0.18);
  border-color: rgba(16,185,129,0.3);
}

.btn-const {
  color: var(--accent-amber);
  background: rgba(245,158,11,0.08);
  border-color: rgba(245,158,11,0.18);
  font-size: 1rem;
}
.btn-const:hover {
  background: rgba(245,158,11,0.18);
  border-color: rgba(245,158,11,0.3);
}

.btn-mode {
  color: var(--text-muted);
  background: rgba(255,255,255,0.04);
  border-color: var(--border);
  font-size: 0.85rem;
  letter-spacing: 0.05em;
}
.btn-mode:hover {
  background: rgba(255,255,255,0.1);
}
.btn-mode-active {
  color: var(--accent-amber) !important;
  background: rgba(245,158,11,0.12) !important;
  border-color: rgba(245,158,11,0.3) !important;
}

/* ── Span Two ─────────────────────────────────────────── */
.span-two {
  grid-column: span 2;
}

/* ── Ripple ───────────────────────────────────────────── */
.ripple {
  position: absolute;
  border-radius: 50%;
  width: 60px;
  height: 60px;
  background: rgba(255,255,255,0.15);
  transform: scale(0);
  animation: ripple-anim 0.45s ease-out forwards;
  pointer-events: none;
  top: 50%;
  left: 50%;
  margin: -30px 0 0 -30px;
}
@keyframes ripple-anim {
  to { transform: scale(3.5); opacity: 0; }
}

/* ── Instructions Panel ───────────────────────────────── */
.instructions {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 22px 20px;
  min-width: 160px;
  box-shadow:
    0 0 0 1px rgba(255,255,255,0.03) inset,
    0 16px 40px rgba(0,0,0,0.4);
  align-self: flex-start;
}

.instructions h2 {
  font-family: var(--font-display);
  font-size: 0.7rem;
  font-weight: 500;
  letter-spacing: 0.18em;
  color: var(--accent-blue);
  text-transform: uppercase;
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
}

.instructions ul {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 7px;
}

.instructions li {
  display: flex;
  align-items: center;
  gap: 10px;
  font-family: var(--font-ui);
  font-size: 0.82rem;
  color: var(--text-muted);
  transition: color 0.15s;
}
.instructions li:hover {
  color: var(--text-primary);
}

.instructions kbd {
  font-family: var(--font-display);
  font-size: 0.72rem;
  background: rgba(255,255,255,0.08);
  border: 1px solid rgba(255,255,255,0.14);
  border-bottom-width: 2px;
  border-radius: 5px;
  padding: 2px 7px;
  color: var(--text-primary);
  min-width: 30px;
  text-align: center;
  display: inline-block;
}

/* ── Hidden ───────────────────────────────────────────── */
.hidden {
  display: none !important;
}

/* ── Responsive ───────────────────────────────────────── */
@media (max-width: 900px) {
  .app-wrapper {
    flex-direction: column;
    align-items: center;
  }
  .instructions {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    width: min(95vw, 720px);
  }
  .instructions ul {
    flex-direction: row;
    flex-wrap: wrap;
    gap: 8px 16px;
  }
}

@media (max-width: 640px) {
  .calculator-grid {
    padding: 14px;
    gap: 7px;
  }
  .sci-grid {
    grid-template-columns: repeat(7, 1fr);
    width: 100%;
  }
  .btn {
    min-height: 46px;
    font-size: 0.82rem;
  }
  .current-operand {
    font-size: 1.7rem;
  }
  .output {
    min-height: 90px;
    padding: 10px 12px 12px;
  }
}

@media (max-width: 480px) {
  body { padding: 10px; }
  .btn {
    min-height: 40px;
    font-size: 0.75rem;
    border-radius: 8px;
  }
  .current-operand {
    font-size: 1.5rem;
  }
}