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

/* ── THEME VARIABLES ── */
:root {
  --bg-page:      linear-gradient(135deg, #0f0c29, #302b63, #24243e);
  --bg-calc:      rgba(18, 18, 32, 0.92);
  --bg-display:   rgba(8, 8, 20, 0.95);
  --bg-sci:       rgba(20, 20, 40, 0.8);
  --border-calc:  rgba(99, 102, 241, 0.2);
  --glow-calc:    rgba(99, 102, 241, 0.12);

  --clr-expr:     #7c7caa;
  --clr-result:   #f0f0ff;
  --clr-op-ind:   #a5b4fc;

  /* button colors */
  --num-bg:       #1e1e38;
  --num-hover:    #2a2a50;
  --num-clr:      #e0e0ff;

  --op-bg:        #1a1040;
  --op-hover:     #2a1a60;
  --op-clr:       #a78bfa;
  --op-active-bg: #3b1fa8;

  --clear-bg:     #2a0a0a;
  --clear-hover:  #3d1010;
  --clear-clr:    #ff6b6b;

  --delete-bg:    #1a1a10;
  --delete-hover: #2a2a18;
  --delete-clr:   #fbbf24;

  --percent-bg:   #0a1a2a;
  --percent-hover:#102a3a;
  --percent-clr:  #38bdf8;

  --sign-bg:      #0a1a1a;
  --sign-hover:   #102828;
  --sign-clr:     #34d399;

  --dot-bg:       #1a1020;
  --dot-hover:    #2a1a30;
  --dot-clr:      #f472b6;

  --equals-bg:    linear-gradient(135deg, #6366f1, #8b5cf6, #ec4899);
  --equals-hover: linear-gradient(135deg, #4f46e5, #7c3aed, #db2777);
  --equals-shadow:rgba(99, 102, 241, 0.5);

  --sci-bg:       #0d1a2a;
  --sci-hover:    #1a2a3a;
  --sci-clr:      #67e8f9;

  --hist-bg:      rgba(18, 18, 32, 0.95);
  --hist-border:  rgba(99, 102, 241, 0.15);
  --hist-item-hov:#1e1e38;
  --hist-expr:    #7c7caa;
  --hist-res:     #e0e0ff;
  --hist-scroll:  #3a3a6e;

  --top-btn-bg:   #1e1e38;
  --top-btn-clr:  #a0a0cc;
  --top-btn-hov:  #2a2a50;
}

[data-theme="light"] {
  --bg-page:      linear-gradient(135deg, #e0e7ff, #f0fdf4, #fdf4ff);
  --bg-calc:      rgba(255, 255, 255, 0.92);
  --bg-display:   rgba(240, 240, 255, 0.95);
  --bg-sci:       rgba(230, 230, 250, 0.9);
  --border-calc:  rgba(99, 102, 241, 0.3);
  --glow-calc:    rgba(99, 102, 241, 0.08);

  --clr-expr:     #6060a0;
  --clr-result:   #1a1a3a;
  --clr-op-ind:   #6366f1;

  --num-bg:       #eef0ff;
  --num-hover:    #dde0ff;
  --num-clr:      #1a1a3a;

  --op-bg:        #ede9fe;
  --op-hover:     #ddd6fe;
  --op-clr:       #7c3aed;
  --op-active-bg: #c4b5fd;

  --clear-bg:     #fee2e2;
  --clear-hover:  #fecaca;
  --clear-clr:    #dc2626;

  --delete-bg:    #fef9c3;
  --delete-hover: #fef08a;
  --delete-clr:   #b45309;

  --percent-bg:   #e0f2fe;
  --percent-hover:#bae6fd;
  --percent-clr:  #0369a1;

  --sign-bg:      #d1fae5;
  --sign-hover:   #a7f3d0;
  --sign-clr:     #065f46;

  --dot-bg:       #fce7f3;
  --dot-hover:    #fbcfe8;
  --dot-clr:      #be185d;

  --equals-bg:    linear-gradient(135deg, #6366f1, #8b5cf6, #ec4899);
  --equals-hover: linear-gradient(135deg, #4f46e5, #7c3aed, #db2777);
  --equals-shadow:rgba(99, 102, 241, 0.4);

  --sci-bg:       #e0f7fa;
  --sci-hover:    #b2ebf2;
  --sci-clr:      #0e7490;

  --hist-bg:      rgba(255, 255, 255, 0.96);
  --hist-border:  rgba(99, 102, 241, 0.2);
  --hist-item-hov:#eef0ff;
  --hist-expr:    #6060a0;
  --hist-res:     #1a1a3a;
  --hist-scroll:  #c4b5fd;

  --top-btn-bg:   #eef0ff;
  --top-btn-clr:  #4a4a8a;
  --top-btn-hov:  #dde0ff;
}

/* ── BODY ── */
body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-page);
  font-family: 'Segoe UI', system-ui, sans-serif;
  transition: background 0.4s;
  padding: 16px;
}

.wrapper {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
  max-width: 400px;
}

/* ── CALCULATOR CARD ── */
.calculator {
  width: 100%;
  max-width: 400px;
  background: var(--bg-calc);
  border-radius: 28px;
  padding: 22px;
  box-shadow:
    0 24px 64px rgba(0,0,0,0.4),
    0 0 0 1px var(--border-calc),
    0 0 50px var(--glow-calc);
  backdrop-filter: blur(16px);
  transition: box-shadow 0.3s, background 0.4s;
}

/* ── TOP BAR ── */
.top-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 14px;
  gap: 8px;
}

.top-right { display: flex; gap: 8px; }

/* shared pill style */
.mode-btn, .hist-toggle, .theme-btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  background: var(--top-btn-bg);
  color: var(--top-btn-clr);
  border: 1px solid transparent;
  border-radius: 22px;
  cursor: pointer;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.3px;
  transition: background 0.2s, color 0.2s, border-color 0.2s, box-shadow 0.2s;
  white-space: nowrap;
}

.mode-btn {
  padding: 7px 14px;
  font-size: 12px;
}

/* icon-only buttons */
.hist-toggle, .theme-btn {
  padding: 7px 10px;
  font-size: 15px;
  border-radius: 50%;
  width: 34px;
  height: 34px;
  justify-content: center;
}

.mode-btn:hover {
  background: var(--top-btn-hov);
  border-color: rgba(99,102,241,0.3);
  box-shadow: 0 2px 10px rgba(99,102,241,0.15);
}

.hist-toggle:hover, .theme-btn:hover {
  background: var(--top-btn-hov);
  border-color: rgba(99,102,241,0.3);
  box-shadow: 0 2px 10px rgba(99,102,241,0.15);
}

.mode-btn.active {
  background: linear-gradient(135deg, #6366f1, #8b5cf6);
  color: #fff;
  border-color: transparent;
  box-shadow: 0 3px 14px rgba(99,102,241,0.45);
}

/* ── DISPLAY ── */
.display {
  background: var(--bg-display);
  border-radius: 18px;
  padding: 14px 18px;
  margin-bottom: 14px;
  min-height: 100px;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  justify-content: flex-end;
  word-break: break-all;
  transition: background 0.4s;
  position: relative;
}

.op-indicator {
  position: absolute;
  top: 12px;
  left: 14px;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 1px;
  text-transform: uppercase;
  color: var(--clr-op-ind);
  opacity: 0;
  transition: opacity 0.3s;
  padding: 2px 8px;
  border-radius: 8px;
  background: rgba(99,102,241,0.12);
}
.op-indicator.show { opacity: 1; }

.expression {
  color: var(--clr-expr);
  font-size: 13px;
  min-height: 18px;
  margin-bottom: 4px;
  transition: color 0.4s;
}

.result {
  color: var(--clr-result);
  font-size: 42px;
  font-weight: 300;
  transition: font-size 0.15s, color 0.4s;
  animation: slideUp 0.18s ease;
}

@keyframes slideUp {
  from { opacity: 0.3; transform: translateY(8px); }
  to   { opacity: 1;   transform: translateY(0); }
}

/* ── SCIENTIFIC BUTTONS ── */
.sci-buttons {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 7px;
  margin-bottom: 12px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease, margin 0.35s ease;
}
.sci-buttons.open {
  max-height: 120px;
  margin-bottom: 12px;
}

/* ── BUTTON GRID ── */
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

/* ── BASE BUTTON ── */
.btn {
  border: none;
  border-radius: 14px;
  padding: 17px 8px;
  font-size: 17px;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s, transform 0.1s, box-shadow 0.15s;
  user-select: none;
  position: relative;
  overflow: hidden;
}
.btn:active { transform: scale(0.93); }

/* ── RIPPLE ── */
.ripple {
  position: absolute;
  border-radius: 50%;
  background: rgba(255,255,255,0.28);
  transform: scale(0);
  animation: ripple 0.5s linear;
  pointer-events: none;
}
@keyframes ripple { to { transform: scale(4); opacity: 0; } }

/* ── BUTTON COLOR GROUPS ── */
.btn-num    { background: var(--num-bg);     color: var(--num-clr); }
.btn-num:hover { background: var(--num-hover); }

.btn-op     { background: var(--op-bg);      color: var(--op-clr); font-size: 20px; }
.btn-op:hover  { background: var(--op-hover); }
.btn-op.op-active { background: var(--op-active-bg); color: #fff; box-shadow: 0 0 12px rgba(99,102,241,0.5); }

.btn-clear  { background: var(--clear-bg);   color: var(--clear-clr); }
.btn-clear:hover { background: var(--clear-hover); }

.btn-delete { background: var(--delete-bg);  color: var(--delete-clr); }
.btn-delete:hover { background: var(--delete-hover); }

.btn-percent { background: var(--percent-bg); color: var(--percent-clr); }
.btn-percent:hover { background: var(--percent-hover); }

.btn-sign   { background: var(--sign-bg);    color: var(--sign-clr); }
.btn-sign:hover { background: var(--sign-hover); }

.btn-dot    { background: var(--dot-bg);     color: var(--dot-clr); font-size: 22px; font-weight: 700; }
.btn-dot:hover { background: var(--dot-hover); }

.btn-equals {
  background: var(--equals-bg);
  color: #fff;
  font-size: 22px;
  box-shadow: 0 4px 20px var(--equals-shadow);
}
.btn-equals:hover {
  background: var(--equals-hover);
  box-shadow: 0 6px 28px var(--equals-shadow);
}

.btn.sci    { background: var(--sci-bg);     color: var(--sci-clr); font-size: 12px; padding: 10px 4px; border-radius: 10px; }
.btn.sci:hover { background: var(--sci-hover); }

.span2 { grid-column: span 2; }

/* ── KEYBOARD HIGHLIGHT ── */
.btn.active { transform: scale(0.93); filter: brightness(1.3); }

/* ── HISTORY PANEL — desktop ── */
.history-panel {
  position: absolute;
  right: calc(100% + 14px);
  top: 0;
  width: 230px;
  background: var(--hist-bg);
  border-radius: 22px;
  padding: 16px;
  box-shadow: 0 20px 60px rgba(0,0,0,0.35), 0 0 0 1px var(--hist-border);
  backdrop-filter: blur(16px);
  max-height: 540px;
  display: flex;
  flex-direction: column;
  opacity: 0;
  transform: translateX(10px);
  pointer-events: none;
  transition: opacity 0.28s ease, transform 0.28s ease, background 0.4s;
  z-index: 100;
}
.history-panel.open { opacity: 1; transform: translateX(0); pointer-events: all; }

/* ── HISTORY OVERLAY backdrop (mobile) ── */
.hist-backdrop {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.5);
  z-index: 199;
  backdrop-filter: blur(2px);
}
.hist-backdrop.show { display: block; }

.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 14px;
  color: var(--hist-res);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.3px;
}
.history-header button {
  background: var(--clear-bg);
  color: var(--clear-clr);
  border: none;
  padding: 5px 11px;
  border-radius: 12px;
  cursor: pointer;
  font-size: 11px;
  font-weight: 600;
  transition: background 0.2s;
}
.history-header button:hover { background: var(--clear-hover); }

#historyList {
  list-style: none;
  overflow-y: auto;
  flex: 1;
  scrollbar-width: thin;
  scrollbar-color: var(--hist-scroll) transparent;
}
#historyList::-webkit-scrollbar { width: 4px; }
#historyList::-webkit-scrollbar-thumb { background: var(--hist-scroll); border-radius: 4px; }

#historyList li {
  padding: 10px 8px;
  border-bottom: 1px solid var(--hist-border);
  cursor: pointer;
  border-radius: 8px;
  transition: background 0.15s;
}
#historyList li:hover { background: var(--hist-item-hov); }
#historyList li .hist-expr   { color: var(--hist-expr); font-size: 11px; }
#historyList li .hist-result { color: var(--hist-res);  font-size: 16px; font-weight: 600; }

.no-history { color: var(--hist-expr); font-size: 12px; text-align: center; margin-top: 20px; }

/* ════════════════════════════════════════
   MOBILE  ≤ 480px
   ════════════════════════════════════════ */
@media (max-width: 480px) {

  body { padding: 10px; align-items: flex-start; padding-top: 20px; }

  .wrapper { max-width: 100%; }

  .calculator {
    border-radius: 22px;
    padding: 16px;
  }

  /* display */
  .display {
    min-height: 88px;
    padding: 12px 14px;
    margin-bottom: 12px;
  }
  .result { font-size: 36px; }
  .expression { font-size: 12px; }
  .op-indicator { font-size: 10px; }

  /* sci grid — 4 cols on mobile */
  .sci-buttons {
    grid-template-columns: repeat(4, 1fr);
    gap: 6px;
  }
  .sci-buttons.open { max-height: 180px; }
  .btn.sci { font-size: 11px; padding: 10px 2px; }

  /* main buttons */
  .buttons { gap: 8px; }
  .btn {
    padding: 16px 6px;
    font-size: 16px;
    border-radius: 12px;
  }
  .btn-op  { font-size: 18px; }
  .btn-dot { font-size: 20px; }
  .btn-equals { font-size: 20px; }

  /* top bar */
  .mode-btn { padding: 6px 10px; font-size: 11px; }
  .hist-toggle, .theme-btn { width: 30px; height: 30px; }

  /* ── HISTORY: full-screen bottom sheet on mobile ── */
  .history-panel {
    position: fixed;
    right: 0;
    left: 0;
    bottom: 0;
    top: auto;
    width: 100%;
    max-height: 65vh;
    border-radius: 22px 22px 0 0;
    transform: translateY(100%);
    opacity: 1;
    z-index: 200;
    padding: 20px 16px 28px;
  }
  .history-panel.open {
    transform: translateY(0);
    pointer-events: all;
  }

  /* drag handle */
  .history-panel::before {
    content: '';
    display: block;
    width: 40px;
    height: 4px;
    background: var(--hist-scroll);
    border-radius: 4px;
    margin: 0 auto 14px;
  }
}