/* ============================================================
   SANDY CALCULATOR — Clean Black & White Theme
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=DM+Mono:wght@400;500&display=swap');

/* ── Design Tokens ── */
:root {
  /* Light mode */
  --bg:          #f5f5f5;
  --surface:     #ffffff;
  --surface-2:   #f0f0f0;
  --border:      #e0e0e0;
  --border-hover:#b0b0b0;
  --text:        #111111;
  --text-muted:  #888888;
  --text-inv:    #ffffff;

  --accent:      #111111;
  --accent-soft: #222222;

  --btn-num-bg:    #ffffff;
  --btn-num-hover: #f0f0f0;
  --btn-op-bg:     #f7f7f7;
  --btn-op-hover:  #ececec;
  --btn-spec-bg:   #f7f7f7;
  --btn-spec-hover:#ececec;
  --btn-clear-bg:  #ffffff;
  --btn-eq-bg:     #111111;
  --btn-eq-text:   #ffffff;
  --btn-eq-hover:  #333333;

  --shadow-card:   0 2px 24px rgba(0,0,0,0.08), 0 1px 4px rgba(0,0,0,0.05);
  --shadow-btn:    0 1px 3px rgba(0,0,0,0.08);
  --shadow-btn-hover: 0 4px 12px rgba(0,0,0,0.12);

  --radius:     16px;
  --radius-sm:  10px;
  --radius-xs:  7px;
  --gap:        10px;
  --btn-h:      clamp(52px, 12vw, 62px);

  --font-ui:    'Inter', system-ui, sans-serif;
  --font-mono:  'DM Mono', 'Menlo', monospace;
  --ease:       cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

/* Dark mode */
body.dark {
  --bg:          #0a0a0a;
  --surface:     #161616;
  --surface-2:   #1e1e1e;
  --border:      #2a2a2a;
  --border-hover:#444444;
  --text:        #f0f0f0;
  --text-muted:  #666666;
  --text-inv:    #111111;

  --accent:      #f0f0f0;
  --accent-soft: #cccccc;

  --btn-num-bg:    #1e1e1e;
  --btn-num-hover: #2a2a2a;
  --btn-op-bg:     #252525;
  --btn-op-hover:  #303030;
  --btn-spec-bg:   #252525;
  --btn-spec-hover:#303030;
  --btn-clear-bg:  #1e1e1e;
  --btn-eq-bg:     #f0f0f0;
  --btn-eq-text:   #111111;
  --btn-eq-hover:  #cccccc;

  --shadow-card:   0 2px 24px rgba(0,0,0,0.5), 0 1px 4px rgba(0,0,0,0.3);
  --shadow-btn:    0 1px 3px rgba(0,0,0,0.3);
  --shadow-btn-hover: 0 4px 12px rgba(0,0,0,0.5);
}

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

html { font-size: 16px; }

body {
  min-height: 100vh;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-ui);
  display: flex;
  flex-direction: column;
  transition: background 0.3s var(--ease), color 0.3s var(--ease);
  -webkit-font-smoothing: antialiased;
}

/* ── App Shell ── */
.app {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* ============================================================
   HEADER
   ============================================================ */
.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 18px clamp(20px, 5vw, 48px);
  border-bottom: 1px solid var(--border);
  background: var(--surface);
  position: sticky;
  top: 0;
  z-index: 100;
  transition: background 0.3s var(--ease), border-color 0.3s var(--ease);
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
}

.brand-icon {
  width: 28px;
  height: 28px;
  color: var(--text);
  flex-shrink: 0;
}

.brand-name {
  font-size: clamp(1rem, 2.5vw, 1.2rem);
  font-weight: 700;
  letter-spacing: -0.5px;
  color: var(--text);
}
.brand-name span {
  font-weight: 300;
  color: var(--text-muted);
}

.header-controls {
  display: flex;
  align-items: center;
  gap: 8px;
}

/* Theme button */
.theme-btn {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition:
    background 0.2s var(--ease),
    border-color 0.2s var(--ease),
    transform 0.2s var(--ease);
}
.theme-btn svg { width: 18px; height: 18px; }
.theme-btn:hover {
  background: var(--border);
  border-color: var(--border-hover);
  transform: rotate(15deg);
}

/* Show correct icon per theme */
.theme-btn .icon-sun  { display: none; }
.theme-btn .icon-moon { display: block; }
body.dark .theme-btn .icon-sun  { display: block; }
body.dark .theme-btn .icon-moon { display: none; }

/* History toggle (mobile only) */
.hist-toggle-btn {
  display: none;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  cursor: pointer;
  align-items: center;
  justify-content: center;
  transition: background 0.2s var(--ease), border-color 0.2s var(--ease);
}
.hist-toggle-btn svg { width: 18px; height: 18px; }
.hist-toggle-btn:hover { background: var(--border); border-color: var(--border-hover); }

/* ============================================================
   MAIN CONTENT
   ============================================================ */
.main-content {
  flex: 1;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  gap: clamp(16px, 2.5vw, 32px);
  padding: clamp(24px, 5vw, 56px) clamp(16px, 4vw, 32px);
  flex-wrap: wrap;
}

/* ============================================================
   CALCULATOR CARD
   ============================================================ */
.calculator {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-card);
  padding: clamp(18px, 4vw, 28px);
  width: min(100%, 360px);
  transition:
    background 0.3s var(--ease),
    border-color 0.3s var(--ease),
    box-shadow 0.3s var(--ease);
}

/* ── Display ── */
.display-wrap {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 16px 18px 14px;
  margin-bottom: 16px;
  min-height: 90px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 6px;
  transition: background 0.3s var(--ease), border-color 0.3s var(--ease);
}

.display-expr {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--text-muted);
  text-align: right;
  min-height: 14px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  letter-spacing: 0.3px;
}

.display-input {
  width: 100%;
  background: transparent;
  border: none;
  outline: none;
  color: var(--text);
  font-family: var(--font-mono);
  font-size: clamp(1.8rem, 6vw, 2.4rem);
  font-weight: 500;
  text-align: right;
  caret-color: transparent;
  padding: 0;
  transition: color 0.3s var(--ease);
}
.display-input::placeholder { color: var(--text-muted); font-weight: 300; }

/* ── Button Grid ── */
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--gap);
}

/* Base button */
.btn {
  height: var(--btn-h);
  border-radius: var(--radius-xs);
  border: 1px solid var(--border);
  background: var(--btn-num-bg);
  color: var(--text);
  font-family: var(--font-ui);
  font-size: clamp(0.95rem, 2.5vw, 1.05rem);
  font-weight: 500;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 4px;
  box-shadow: var(--shadow-btn);
  transition:
    background 0.15s var(--ease),
    border-color 0.15s var(--ease),
    box-shadow 0.15s var(--ease),
    transform 0.1s var(--ease);
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}
.btn svg { width: 18px; height: 18px; pointer-events: none; }

.btn:hover {
  background: var(--btn-num-hover);
  border-color: var(--border-hover);
  box-shadow: var(--shadow-btn-hover);
}
.btn:active {
  transform: scale(0.94);
  box-shadow: none;
}

/* Number buttons */
.btn-num {
  background: var(--btn-num-bg);
  font-family: var(--font-mono);
  font-size: clamp(1rem, 2.8vw, 1.15rem);
  font-weight: 500;
  letter-spacing: -0.3px;
}
.btn-num:hover { background: var(--btn-num-hover); }

/* Operator buttons (+, -, ×, ÷) */
.btn-operator {
  background: var(--btn-op-bg);
  color: var(--text);
  border-color: var(--border);
}
.btn-operator:hover { background: var(--btn-op-hover); }
.btn-operator svg { width: 20px; height: 20px; }

/* Special buttons (%, x², √) */
.btn-special {
  background: var(--btn-spec-bg);
  color: var(--text-muted);
  font-size: clamp(0.8rem, 2vw, 0.9rem);
  font-family: var(--font-mono);
  letter-spacing: -0.2px;
}
.btn-special:hover {
  background: var(--btn-spec-hover);
  color: var(--text);
}

/* Clear button */
.btn-clear {
  color: #c0392b;
  background: var(--btn-clear-bg);
  border-color: rgba(192,57,43,0.2);
  font-weight: 600;
}
.btn-clear:hover {
  background: rgba(192,57,43,0.06);
  border-color: rgba(192,57,43,0.4);
}
body.dark .btn-clear { color: #e74c3c; border-color: rgba(231,76,60,0.25); }
body.dark .btn-clear:hover { background: rgba(231,76,60,0.1); border-color: rgba(231,76,60,0.4); }

/* Backspace */
.btn-backspace {
  background: var(--btn-spec-bg);
  color: var(--text-muted);
}
.btn-backspace:hover { background: var(--btn-spec-hover); color: var(--text); }
.btn-backspace svg { width: 20px; height: 20px; }

/* 0 key spans 2 cols */
.btn-zero { grid-column: span 2; justify-content: flex-start; padding-left: 22px; }

/* Equals button */
.btn-equal {
  grid-column: span 4;
  height: calc(var(--btn-h) * 1.05);
  background: var(--btn-eq-bg);
  color: var(--btn-eq-text);
  border: none;
  font-size: clamp(1rem, 3vw, 1.1rem);
  font-weight: 600;
  letter-spacing: 0.5px;
  box-shadow: 0 2px 12px rgba(0,0,0,0.18);
  transition:
    background 0.15s var(--ease),
    box-shadow 0.15s var(--ease),
    transform 0.1s var(--ease);
}
.btn-equal svg { width: 22px; height: 22px; }
.btn-equal:hover {
  background: var(--btn-eq-hover);
  box-shadow: 0 4px 20px rgba(0,0,0,0.22);
}
.btn-equal:active {
  transform: scale(0.97);
  box-shadow: 0 1px 6px rgba(0,0,0,0.15);
}

/* ============================================================
   HISTORY PANEL
   ============================================================ */
.history-panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  width: min(100%, 260px);
  max-height: 540px;
  display: flex;
  flex-direction: column;
  gap: 14px;
  box-shadow: var(--shadow-card);
  transition:
    background 0.3s var(--ease),
    border-color 0.3s var(--ease);
}

.history-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
}

.history-title {
  display: flex;
  align-items: center;
  gap: 7px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text);
  letter-spacing: 0.3px;
  text-transform: uppercase;
}
.history-title svg { width: 15px; height: 15px; color: var(--text-muted); }

.hist-clear-btn {
  display: flex;
  align-items: center;
  gap: 5px;
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: var(--radius-xs);
  padding: 5px 10px;
  font-family: var(--font-ui);
  font-size: 0.75rem;
  cursor: pointer;
  transition: background 0.15s var(--ease), color 0.15s var(--ease), border-color 0.15s var(--ease);
}
.hist-clear-btn svg { width: 13px; height: 13px; }
.hist-clear-btn:hover {
  background: rgba(192,57,43,0.06);
  border-color: rgba(192,57,43,0.35);
  color: #c0392b;
}
body.dark .hist-clear-btn:hover {
  background: rgba(231,76,60,0.08);
  border-color: rgba(231,76,60,0.35);
  color: #e74c3c;
}

.history-list {
  list-style: none;
  overflow-y: auto;
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 6px;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}
.history-list::-webkit-scrollbar { width: 3px; }
.history-list::-webkit-scrollbar-track { background: transparent; }
.history-list::-webkit-scrollbar-thumb { background: var(--border); border-radius: 99px; }

.history-list li {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--text);
  padding: 10px 12px;
  border-radius: var(--radius-xs);
  background: var(--surface-2);
  border: 1px solid var(--border);
  cursor: pointer;
  word-break: break-all;
  line-height: 1.6;
  transition: background 0.15s var(--ease), border-color 0.15s var(--ease);
}
.history-list li:hover {
  background: var(--btn-op-hover);
  border-color: var(--border-hover);
}
.history-list li .hist-result {
  font-weight: 500;
  font-size: 0.9rem;
  display: block;
  margin-top: 2px;
}
.history-list li .hist-time {
  font-size: 0.68rem;
  color: var(--text-muted);
  display: block;
  margin-top: 2px;
}

.history-empty {
  font-size: 0.8rem !important;
  color: var(--text-muted) !important;
  text-align: center;
  cursor: default !important;
  padding: 20px 0 !important;
  background: transparent !important;
  border-color: transparent !important;
}
.history-empty:hover { background: transparent !important; border-color: transparent !important; }

/* ── Footer ── */
.app-footer {
  text-align: center;
  padding: 18px;
  font-size: 0.8rem;
  color: var(--text-muted);
  border-top: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 5px;
  flex-wrap: wrap;
  transition: border-color 0.3s var(--ease);
}
.app-footer strong { color: var(--text); font-weight: 600; }
.footer-heart {
  width: 14px;
  height: 14px;
  color: #c0392b;
  flex-shrink: 0;
}
body.dark .footer-heart { color: #e74c3c; }

/* ── Error shake ── */
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20%       { transform: translateX(-6px); }
  40%       { transform: translateX(6px); }
  60%       { transform: translateX(-4px); }
  80%       { transform: translateX(4px); }
}
.shake { animation: shake 0.38s var(--ease); }

/* ============================================================
   RESPONSIVE
   ============================================================ */

/* Tablet & below: stack, hide history */
@media (max-width: 760px) {
  .main-content {
    flex-direction: column;
    align-items: center;
    padding: 20px 16px;
  }

  .calculator { width: min(100%, 400px); }

  .history-panel {
    width: min(100%, 400px);
    max-height: 200px;
    display: none;
  }
  .history-panel.panel-open { display: flex; }

  .hist-toggle-btn { display: flex; }
}

/* Small phones */
@media (max-width: 400px) {
  :root {
    --btn-h: 54px;
    --gap: 8px;
  }
  .calculator { padding: 14px 12px; border-radius: 12px; }
  .display-input { font-size: 1.7rem; }
  .brand-name { font-size: 0.95rem; }
}

/* Very small */
@media (max-width: 340px) {
  :root { --btn-h: 48px; --gap: 6px; }
  .display-input { font-size: 1.5rem; }
}

/* Wide screens: always show history beside */
@media (min-width: 860px) {
  .main-content {
    align-items: center;
    flex-wrap: nowrap;
  }
  .history-panel { display: flex; }
}