:root {
  --glass-bg: rgba(255, 255, 255, .08);
  --glass-brd: rgba(255, 255, 255, .2);
  --txt: #eaf6ff;
  --muted: #a7b3c0;
  --neon-green: #6cffb1;
  --neon-blue: #7ad0ff;
  --neon-pink: #ff6ad5;
  --btn-bg: rgba(255, 255, 255, .06);
  --btn-brd: rgba(255, 255, 255, .16);
  --shadow: 0 20px 60px rgba(0, 0, 0, .35);
  --radius: 22px;
}

* {
  box-sizing: border-box
}

html,
body {
  height: 100%
}

body {
  margin: 0;
  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "Apple Color Emoji", "Segoe UI Emoji";
  background: radial-gradient(1200px 800px at 10% -10%, #111 30%, #0a0f17 60%, #0b1424 100%),
    radial-gradient(800px 600px at 120% 120%, #0b1424, #081220);
  color: var(--txt);
  display: grid;
  place-items: center;
  padding: 24px;
}

body {
  margin: 0;
  padding: 0;
  height: 100vh;
  width: 100vw;

  font-family: "Poppins", ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "Apple Color Emoji", "Segoe UI Emoji";
  color: var(--txt);

  display: flex;
  justify-content: center;
  align-items: center;

  /* Background image – responsive */
  background: url("bg.jpg") no-repeat center center;
  background-size: cover;
  /* ensures it covers full screen */
  background-attachment: fixed;
  /* makes it stable while scrolling */
}

.app {
  width: min(780px, 100%);
  display: grid;
  grid-template-columns: 1fr 320px;
  gap: 18px;
}

@media (max-width: 860px) {
  .app {
    grid-template-columns: 1fr
  }
}

.calc {
  background: var(--glass-bg);
  border: 1px solid var(--glass-brd);
  backdrop-filter: blur(16px) saturate(130%);
  -webkit-backdrop-filter: blur(16px) saturate(130%);
  border-radius: var(--radius);
  box-shadow: var(--txt);
  padding: 20px;
}

.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}

.display-wrap {
  position: relative;
  background: linear-gradient(180deg, rgba(255, 255, 255, .06), rgba(255, 255, 255, .02));
  border: 1px solid var(--glass-brd);
  border-radius: 16px;
  padding: 16px;
  min-height: 88px;
  overflow: hidden;
}

.display {
  width: 100%;
  background: transparent;
  border: none;
  outline: none;
  color: var(--txt);
  font-size: 34px;
  text-align: right;
  letter-spacing: .02em;
}

.ghost {
  position: absolute;
  right: 16px;
  bottom: 10px;
  color: var(--txt);
  font-size: 15px;
  opacity: .85;
}

/* slide-in animation for result */
.slide-in {
  animation: slideIn .28s cubic-bezier(.2, .7, .2, 1)
}

@keyframes slideIn {
  from {
    transform: translateX(18px);
    opacity: .4
  }

  to {
    transform: none;
    opacity: 1
  }
}

.grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin-top: 16px;
}

button.key {
  position: relative;
  border: 1px solid var(--btn-brd);
  background: var(--btn-bg);
  color: var(--txt);
  padding: 18px 12px;
  border-radius: 16px;
  font-size: 18px;
  cursor: pointer;
  overflow: hidden;
  transition: transform .08s ease, box-shadow .2s ease, border-color .2s ease;
  box-shadow: inset 0 0 0 0 rgba(255, 255, 255, .08), 0 8px 28px rgba(0, 0, 0, .25);
  user-select: none;
}

button.key:active {
  transform: scale(.98)
}

/* neon categories */
.op {
  box-shadow: 0 0 0 1px rgba(122, 208, 255, .15), 0 0 22px rgba(122, 208, 255, .35) inset
}

.op:hover {
  border-color: rgba(122, 208, 255, .8)
}

.num {
  box-shadow: 0 0 0 1px rgba(108, 255, 177, .12), 0 0 18px rgba(108, 255, 177, .28) inset
}

.num:hover {
  border-color: rgba(108, 255, 177, .7)
}

.accent {
  background: linear-gradient(135deg, rgba(255, 106, 213, .18), rgba(122, 208, 255, .18));
  border-color: rgba(255, 255, 255, .22);
}

.span-2 {
  grid-column: span 2
}

/* Ripple */
.ripple {
  position: absolute;
  inset: auto;
  border-radius: 50%;
  transform: translate(-50%, -50%);
  pointer-events: none;
  opacity: .65;
  background: radial-gradient(circle, rgba(255, 255, 255, .9) 0%, rgba(255, 255, 255, .05) 60%, transparent 70%);
  animation: ripple .6s ease-out forwards;
}

@keyframes ripple {
  from {
    width: 0;
    height: 0;
    opacity: .65
  }

  to {
    width: 260px;
    height: 260px;
    opacity: 0
  }
}

/* History Panel */
.history {
  position: relative;
  background: var(--glass-bg);
  border: 1px solid var(--glass-brd);
  backdrop-filter: blur(16px) saturate(130%);
  -webkit-backdrop-filter: blur(16px) saturate(130%);
  border-radius: var(--radius);
  box-shadow: var(--txt);
  padding: 18px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  max-height: 560px;
}

.history h3 {
  margin: 0;
  color: var(--txt);
  font-weight: 600;
  letter-spacing: .06em
}

.history-list {
  list-style: none;
  margin: 0;
  padding: 0;
  overflow: auto;
  scrollbar-width: thin;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.history-item {
  border: 1px solid var(--btn-brd);
  border-radius: 14px;
  padding: 10px 12px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  background: linear-gradient(180deg, rgba(255, 255, 255, .05), rgba(255, 255, 255, .02));
  transition: border-color .2s ease, background .2s ease;
}

.history-item:hover {
  border-color: rgba(122, 208, 255, .6)
}

.expr {
  color: #a6bdd6;
  font-size: 14px
}

.res {
  color: #a6bdd6;
  font-weight: 700
}

.controls {
  display: flex;
  gap: 8px
}

.chip {
  border: 2px solid var(--btn-brd);
  background: var(--btn-bg);
  color: var(--txt);
  padding: 8px 12px;
  border-radius: 999px;
  font-size: 14px;
  cursor: pointer
}

.chip:hover {
  border-color: rgba(255, 255, 255, .35)
}

/* utility */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0
}