styles.css

:root {
  --bg: #0b0b14;
  --text: #f5f5f7;
  --muted: rgba(245, 245, 247, 0.55);
  --glass: rgba(22, 22, 38, 0.55);
  --panel: #12121f;
  --edge: rgba(255, 255, 255, 0.1);
  --key: rgba(255, 255, 255, 0.06);
  --key-hover: rgba(255, 255, 255, 0.11);
  --key-edge: rgba(255, 255, 255, 0.06);
  --key-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.06), 0 6px 14px rgba(0, 0, 0, 0.25);
  --fn: rgba(255, 255, 255, 0.13);
  --op: rgba(139, 92, 246, 0.2);
  --op-hover: rgba(139, 92, 246, 0.3);
  --op-text: #c4b5fd;
  --accent: linear-gradient(135deg, #8b5cf6, #ec4899);
  --accent-glow: rgba(236, 72, 153, 0.35);
  --blob-1: #7c3aed;
  --blob-2: #db2777;
  --blob-3: #0891b2;
  --blob-opacity: 0.7;
  --shadow: 0 30px 80px rgba(0, 0, 0, 0.55);
  --danger: #fda4af;
  --ease: cubic-bezier(0.2, 0.8, 0.2, 1);
  color-scheme: dark;
  font-family: "Space Grotesk", system-ui, -apple-system, "Segoe UI", sans-serif;
}

/* Light keeps a nod to the original neumorphic look: soft raised keys on a pale surface. */
:root[data-theme="light"] {
  --bg: #eef0f7;
  --text: #1e1b2e;
  --muted: rgba(30, 27, 46, 0.55);
  --glass: rgba(255, 255, 255, 0.55);
  --panel: #f8f8fd;
  --edge: rgba(255, 255, 255, 0.85);
  --key: #f4f5fb;
  --key-hover: #ffffff;
  --key-edge: rgba(255, 255, 255, 0.9);
  --key-shadow: -4px -4px 10px rgba(255, 255, 255, 0.9), 4px 4px 12px rgba(80, 70, 140, 0.16);
  --fn: #e5e7f2;
  --op: rgba(139, 92, 246, 0.14);
  --op-hover: rgba(139, 92, 246, 0.22);
  --op-text: #6d28d9;
  --accent-glow: rgba(236, 72, 153, 0.3);
  --blob-1: #a78bfa;
  --blob-2: #f9a8d4;
  --blob-3: #67e8f9;
  --blob-opacity: 0.55;
  --shadow: 0 30px 70px rgba(76, 64, 140, 0.25);
  --danger: #e11d48;
  color-scheme: light;
}

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

[hidden] {
  display: none !important;
}

body {
  margin: 0;
  min-height: 100dvh;
  display: grid;
  place-items: center;
  overflow-x: hidden;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
}

button {
  font: inherit;
  color: inherit;
}

:focus-visible {
  outline: 2px solid #a78bfa;
  outline-offset: 3px;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

svg {
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

/* ============ Moving colour behind the glass ============ */

.backdrop {
  position: fixed;
  inset: 0;
  z-index: -1;
  overflow: hidden;
  filter: blur(80px);
  opacity: var(--blob-opacity);
}
.backdrop i {
  position: absolute;
  width: 46vmax;
  height: 46vmax;
  border-radius: 50%;
  animation: float 22s ease-in-out infinite alternate;
}
.backdrop i:nth-child(1) {
  top: -14vmax;
  left: -12vmax;
  background: var(--blob-1);
}
.backdrop i:nth-child(2) {
  right: -14vmax;
  bottom: -18vmax;
  background: var(--blob-2);
  animation-duration: 27s;
  animation-delay: -7s;
}
.backdrop i:nth-child(3) {
  top: 38%;
  left: 52%;
  width: 30vmax;
  height: 30vmax;
  background: var(--blob-3);
  opacity: 0.7;
  animation-duration: 31s;
  animation-delay: -13s;
}

/* ============ The calculator ============ */

.stage {
  width: 100%;
  display: grid;
  justify-items: center;
  gap: 20px;
  padding: 24px 16px;
  perspective: 1400px;
}

.calc {
  position: relative;
  width: min(380px, 100%);
  padding: 18px 20px 22px;
  overflow: hidden;
  border: 1px solid var(--edge);
  border-radius: 38px;
  background: var(--glass);
  -webkit-backdrop-filter: blur(28px) saturate(160%);
  backdrop-filter: blur(28px) saturate(160%);
  box-shadow: var(--shadow);
  transform: rotateX(var(--rx, 0deg)) rotateY(var(--ry, 0deg));
  transition:
    transform 0.3s ease-out,
    background-color 0.5s;
  animation: arrive 0.9s var(--ease) backwards;
}

/* A soft highlight that follows the pointer across the glass. */
.shine {
  position: absolute;
  inset: 0;
  pointer-events: none;
  background: radial-gradient(520px circle at var(--mx, 50%) var(--my, 0%), rgba(255, 255, 255, 0.13), transparent 42%);
  opacity: 0;
  transition: opacity 0.4s;
}
.calc.lit .shine {
  opacity: 1;
}

.calc-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.brand {
  color: var(--muted);
  font-size: 0.85rem;
  letter-spacing: 0.3em;
  text-transform: uppercase;
}
.chip {
  display: grid;
  place-items: center;
  width: 40px;
  height: 40px;
  padding: 0;
  border: 1px solid var(--key-edge);
  border-radius: 50%;
  background: var(--key);
  cursor: pointer;
  transition:
    background-color 0.2s,
    transform 0.2s var(--ease);
}
.chip:hover {
  background: var(--key-hover);
  transform: rotate(-12deg);
}
.chip svg {
  width: 18px;
  height: 18px;
}
:root[data-theme="light"] .sun,
:root:not([data-theme="light"]) .moon {
  display: none;
}

/* ============ Display ============ */

.display {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  justify-content: flex-end;
  gap: 2px;
  min-height: 158px;
  padding: 8px 6px 18px;
  text-align: right;
}
.equation {
  max-width: 100%;
  min-height: 1.4em;
  overflow: hidden;
  color: var(--muted);
  font-size: 1.05rem;
  white-space: nowrap;
  text-overflow: ellipsis;
}
.main {
  display: block;
  width: 100%;
  overflow-x: auto;
  scrollbar-width: none;
  font-size: var(--size, 60px);
  font-weight: 300;
  line-height: 1.15;
  letter-spacing: -0.02em;
  white-space: nowrap;
  font-variant-numeric: tabular-nums;
  cursor: copy;
}
.main::-webkit-scrollbar {
  display: none;
}
.preview {
  min-height: 1.5em;
  color: var(--muted);
  font-size: 1.3rem;
  transition: color 0.2s;
}
.preview.error {
  color: var(--danger);
  font-size: 1.05rem;
}
.display.commit .main {
  transform-origin: right bottom;
  animation: commit 0.5s cubic-bezier(0.2, 0.9, 0.3, 1.25);
}
.display.commit .equation {
  animation: rise-in 0.45s var(--ease) both;
}
.display.shake {
  animation: shake 0.4s ease;
}

.copied {
  position: absolute;
  top: 6px;
  left: 50%;
  padding: 5px 12px;
  border-radius: 999px;
  background: var(--text);
  color: var(--bg);
  font-size: 0.8rem;
  opacity: 0;
  translate: -50% 0;
  pointer-events: none;
}
.copied.show {
  animation: note 1.4s var(--ease) both;
}

/* ============ Keys ============ */

.keypad {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 12px;
}
.keypad button {
  position: relative;
  overflow: hidden;
  aspect-ratio: 1;
  padding: 0;
  border: 1px solid var(--key-edge);
  border-radius: 26px;
  background: var(--key);
  box-shadow: var(--key-shadow);
  font-size: 1.55rem;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
  transition:
    transform 0.12s ease,
    background-color 0.2s,
    box-shadow 0.2s;
  animation: key-in 0.55s var(--ease) backwards;
  animation-delay: calc(var(--i, 0) * 22ms + 250ms);
}
.keypad button:hover {
  background: var(--key-hover);
}
.keypad button:active,
.keypad button.pressed {
  transform: scale(0.92);
}
.keypad .fn {
  background: var(--fn);
  font-size: 1.2rem;
}
.keypad .fn svg {
  width: 24px;
  height: 24px;
  vertical-align: middle;
}
.keypad .op {
  background: var(--op);
  color: var(--op-text);
  font-size: 1.8rem;
}
.keypad .op:hover {
  background: var(--op-hover);
}
.keypad .eq {
  border-color: transparent;
  background: var(--accent);
  color: #fff;
  font-size: 1.9rem;
  box-shadow: 0 10px 30px var(--accent-glow);
}
.keypad .eq:hover {
  filter: brightness(1.08);
}
.ripple {
  position: absolute;
  left: var(--x);
  top: var(--y);
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: currentColor;
  opacity: 0.25;
  pointer-events: none;
  transform: translate(-50%, -50%) scale(0);
  animation: ripple 0.55s ease-out forwards;
}

/* ============ History drawer ============ */

.history {
  position: absolute;
  inset: 70px 12px 12px;
  z-index: 2;
  display: flex;
  flex-direction: column;
  padding: 16px;
  border: 1px solid var(--edge);
  border-radius: 28px;
  background: var(--panel);
  transform: translateY(calc(100% + 30px));
  transition: transform 0.5s var(--ease);
}
.history.open {
  transform: none;
}
.history header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 8px;
}
.history h2 {
  margin: 0;
  font-size: 1rem;
  font-weight: 500;
}
.text-btn {
  padding: 6px 10px;
  border: 0;
  border-radius: 10px;
  background: none;
  color: var(--op-text);
  cursor: pointer;
}
.text-btn:hover {
  background: var(--key-hover);
}
.text-btn:disabled {
  opacity: 0.4;
  cursor: default;
}
.history ol {
  flex: 1;
  margin: 0;
  padding: 0;
  overflow-y: auto;
  list-style: none;
}
.history li button {
  display: block;
  width: 100%;
  padding: 10px 8px;
  border: 0;
  border-radius: 14px;
  background: none;
  text-align: right;
  cursor: pointer;
}
.history li button:hover {
  background: var(--key-hover);
}
.history.open li {
  animation: key-in 0.45s var(--ease) backwards;
  animation-delay: calc(var(--i) * 35ms + 150ms);
}
.h-sum {
  display: block;
  color: var(--muted);
  font-size: 0.9rem;
}
.h-result {
  font-size: 1.4rem;
}
.history-empty {
  margin: auto;
  color: var(--muted);
}

.hint {
  max-width: 380px;
  margin: 0;
  color: var(--muted);
  font-size: 0.85rem;
  line-height: 1.8;
  text-align: center;
}
kbd {
  padding: 1px 6px;
  border: 1px solid var(--edge);
  border-radius: 6px;
  background: var(--key);
  font: inherit;
  font-size: 0.8rem;
}
@media (hover: none) {
  .hint {
    display: none;
  }
}

/* ============ Theme switch: the new theme grows out of the button ============ */

::view-transition-old(root) {
  animation: none;
}
::view-transition-new(root) {
  animation: reveal 0.6s ease-in-out;
}

/* ============ Keyframes ============ */

@keyframes float {
  0% {
    transform: translate(0, 0) scale(1);
  }
  50% {
    transform: translate(8vmax, 6vmax) scale(1.15);
  }
  100% {
    transform: translate(-6vmax, 10vmax) scale(0.9);
  }
}
@keyframes arrive {
  from {
    opacity: 0;
    transform: translateY(40px) rotateX(20deg) scale(0.95);
  }
}
@keyframes key-in {
  from {
    opacity: 0;
    transform: translateY(14px) scale(0.9);
  }
}
@keyframes ripple {
  to {
    opacity: 0;
    transform: translate(-50%, -50%) scale(16);
  }
}
@keyframes commit {
  from {
    opacity: 0.3;
    transform: translateY(45%) scale(0.5);
  }
}
@keyframes rise-in {
  from {
    opacity: 0;
    transform: translateY(14px);
  }
}
@keyframes shake {
  20%,
  60% {
    transform: translateX(-8px);
  }
  40%,
  80% {
    transform: translateX(8px);
  }
}
@keyframes note {
  0% {
    opacity: 0;
    transform: translateY(-6px);
  }
  15%,
  80% {
    opacity: 1;
    transform: none;
  }
  100% {
    opacity: 0;
  }
}
@keyframes reveal {
  from {
    clip-path: circle(0 at var(--reveal-x, 50%) var(--reveal-y, 0));
  }
  to {
    clip-path: circle(150vmax at var(--reveal-x, 50%) var(--reveal-y, 0));
  }
}

@media (max-width: 380px) {
  .calc {
    padding: 14px 14px 16px;
    border-radius: 30px;
  }
  .keypad {
    gap: 9px;
  }
  .keypad button {
    border-radius: 20px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation: none !important;
    transition-duration: 0.01ms !important;
  }
}