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

:root {
    --font-display: 'Space Mono', monospace;
    --font-ui:      'DM Sans', sans-serif;

    /* Background */
    --bg-page:   #0d0d12;
    --bg-calc:   #16161e;
    --bg-display:#0a0a10;

    /* Button surfaces */
    --btn-num:   #1e1e28;
    --btn-num-hover: #272733;
    --btn-sci:   #1a1a26;
    --btn-sci-hover: #22223a;
    --btn-op:    #1f2035;
    --btn-op-hover: #282a48;

    /* Accents */
    --accent-blue:   #009ee8;
    --accent-blue-h: #6ba0ff;
    --accent-red:    #f75f5f;
    --accent-red-h:  #ff7b7b;
    --accent-teal:   #38d9c0;
    --accent-yellow: #f7c948;

    /* Text */
    --text-primary:   #f0f0f8;
    --text-secondary: #8888aa;
    --text-dim:       #55556a;

    /* Borders */
    --border: rgba(255,255,255,0.06);
    --border-active: rgba(255,255,255,0.12);

    /* Sizes */
    --btn-radius: 10px;
    --calc-radius: 20px;
    --gap: 6px;
    --btn-size: 58px;
}

/* ── Body & Page ── */
html, body {
    height: 100%;
    overflow: hidden;
}

body {
    font-family: var(--font-ui);
    background: var(--bg-page);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 16px;
    /* subtle radial glow */
    background-image:
        radial-gradient(ellipse 60% 50% at 50% 0%, rgba(79,142,247,0.08) 0%, transparent 70%),
        radial-gradient(ellipse 40% 30% at 80% 80%, rgba(56,217,192,0.05) 0%, transparent 60%);
}

/* Calculator Wrapper */
.calculator-wrapper {
    display: flex;
    flex-direction: column;
    gap: 10px;
    width: 100%;
    max-width: 480px;
}

/* Header */
.calc-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 4px;
}

.calc-brand {
    font-family: var(--font-display);
    font-size: 0.85rem;
    color: var(--text-dim);
    letter-spacing: 0.15em;
    text-transform: lowercase;
}

.mode-pill {
    font-family: var(--font-display);
    font-size: 0.65rem;
    letter-spacing: 0.12em;
    padding: 3px 10px;
    border-radius: 99px;
    background: rgba(79,142,247,0.12);
    color: var(--accent-blue);
    border: 1px solid rgba(79,142,247,0.25);
    transition: all 0.2s;
}

.mode-pill.rad {
    background: rgba(56,217,192,0.12);
    color: var(--accent-teal);
    border-color: rgba(56,217,192,0.25);
}

/* ── Calculator Grid ─── */
.calculator-grid {
    background: var(--bg-calc);
    border-radius: var(--calc-radius);
    border: 1px solid var(--border);
    padding: 14px;
    display: flex;
    flex-direction: column;
    gap: var(--gap);
    box-shadow:
        0 0 0 1px rgba(255,255,255,0.03),
        0 24px 60px rgba(0,0,0,0.6),
        0 4px 16px rgba(0,0,0,0.4);
}

/* ── Sci Panel ──── */
.sci-panel {
    display: flex;
    flex-direction: column;
    gap: var(--gap);
}

.sci-row {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: var(--gap);
}

.sci-row:last-child {
    grid-template-columns: repeat(5, 1fr);
}

/* ── Numeric Grid ─ */
.num-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr) 1fr;
    grid-template-rows: repeat(4, var(--btn-size));
    grid-template-areas:
        "n7  n8  n9  ndiv  nplus"
        "n4  n5  n6  nmul  nplus"
        "n1  n2  n3  nsub  nplus"
        "ndot n0  neq  neq   ndel";
    gap: var(--gap);
}

.n7    { grid-area: n7;    }
.n8    { grid-area: n8;    }
.n9    { grid-area: n9;    }
.ndiv  { grid-area: ndiv;  }
.nplus { grid-area: nplus; }
.n4    { grid-area: n4;    }
.n5    { grid-area: n5;    }
.n6    { grid-area: n6;    }
.nmul  { grid-area: nmul;  }
.n1    { grid-area: n1;    }
.n2    { grid-area: n2;    }
.n3    { grid-area: n3;    }
.nsub  { grid-area: nsub;  }
.ndot  { grid-area: ndot;  }
.n0    { grid-area: n0;    }
.neq   { grid-area: neq;   }
.ndel  { grid-area: ndel;  }

/* + spans 3 rows vertically */
.plus-btn {
    height: 100%;
}

/* equals spans 2 columns — handled by grid-area */
.equals-btn {
    width: 100%;
    height: 100%;
}

/* ── Display ────── */
.display {
    grid-column: 1 / -1;
    background: var(--bg-display);
    border-radius: 12px;
    border: 1px solid var(--border);
    padding: 16px 18px 14px;
    min-height: 110px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: flex-end;
    gap: 2px;
    overflow: hidden;
    margin-bottom: 4px;
}

.expression-row {
    font-family: var(--font-display);
    font-size: 0.72rem;
    color: var(--text-dim);
    letter-spacing: 0.04em;
    min-height: 1.2em;
    word-break: break-all;
    text-align: right;
    transition: opacity 0.2s;
}

.previous-operand {
    font-family: var(--font-display);
    font-size: 1rem;
    color: var(--text-secondary);
    min-height: 1.4em;
    word-break: break-all;
    text-align: right;
    transition: all 0.15s;
}

.current-operand {
    font-family: var(--font-display);
    font-size: 2.4rem;
    color: var(--text-primary);
    word-break: break-all;
    text-align: right;
    display: flex;
    align-items: center;
    gap: 1px;
    line-height: 1.1;
    transition: font-size 0.15s;
}

.current-operand.shrink { font-size: 1.6rem; }
.current-operand.tiny   { font-size: 1.2rem; }

#current-value { flex: 1; text-align: right; }

/* Blinking caret */
.caret {
    color: var(--accent-blue);
    font-weight: 300;
    animation: blink-caret 1s step-end infinite;
    opacity: 1;
}

@keyframes blink-caret {
    0%, 100% { opacity: 0.6; }
    50%       { opacity: 0; }
}

/* Error state */
.display.error .current-operand {
    color: var(--accent-red);
}

/* ── Base Button ── */
.btn {
    height: var(--btn-size);
    border: 1px solid var(--border);
    border-radius: var(--btn-radius);
    cursor: pointer;
    font-family: var(--font-ui);
    font-size: 0.95rem;
    font-weight: 400;
    color: var(--text-primary);
    background: var(--btn-num);
    outline: none;
    transition:
        background 0.12s,
        transform 0.08s,
        box-shadow 0.12s,
        border-color 0.12s;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
    position: relative;
    overflow: hidden;
}

.btn:hover {
    background: var(--btn-num-hover);
    border-color: var(--border-active);
}

.btn:active {
    transform: scale(0.93);
    box-shadow: none;
}

/* Ripple on click */
.btn::after {
    content: '';
    position: absolute;
    inset: 0;
    background: rgba(255,255,255,0.07);
    opacity: 0;
    border-radius: inherit;
    transition: opacity 0.15s;
}
.btn:active::after { opacity: 1; }

/* equals spans 2 cols — handled via grid-template-areas in .num-grid */

/* ── Number Buttons ──── */
.num-btn {
    background: var(--btn-num);
    font-family: var(--font-display);
    font-size: 1.1rem;
    color: var(--text-primary);
}
.num-btn:hover { background: var(--btn-num-hover); }

.dot-btn   { font-size: 1.4rem; line-height: 1; }

/* ── Operator Buttons ── */
.op-btn {
    background: var(--btn-op);
    color: var(--accent-blue);
    font-family: var(--font-display);
    font-size: 1.2rem;
    border-color: rgba(79,142,247,0.15);
    font-weight: 700;
}
.op-btn:hover {
    background: var(--btn-op-hover);
    border-color: rgba(79,142,247,0.3);
    box-shadow: 0 0 12px rgba(79,142,247,0.1);
}

.plus-btn { grid-column: span 3; }

/* ── Scientific Buttons  */
.sci-btn {
    background: var(--btn-sci);
    color: var(--accent-teal);
    font-size: 0.78rem;
    font-weight: 400;
    border-color: rgba(56,217,192,0.1);
    letter-spacing: 0.01em;
}
.sci-btn:hover {
    background: var(--btn-sci-hover);
    border-color: rgba(56,217,192,0.25);
    box-shadow: 0 0 10px rgba(56,217,192,0.08);
}

/* ── Top Row Buttons ─── */
.top-btn {
    background: var(--btn-sci);
    font-size: 0.82rem;
    color: var(--text-secondary);
}
.top-btn:hover {
    background: var(--btn-sci-hover);
    color: var(--text-primary);
}

.const-btn {
    color: var(--accent-yellow);
    border-color: rgba(247,201,72,0.12);
}
.const-btn:hover {
    border-color: rgba(247,201,72,0.3);
    box-shadow: 0 0 10px rgba(247,201,72,0.08);
}

.bracket-btn { color: var(--text-secondary); font-family: var(--font-display); }

.mode-btn {
    font-family: var(--font-display);
    font-size: 0.65rem;
    letter-spacing: 0.1em;
    color: var(--accent-blue);
    border-color: rgba(79,142,247,0.2);
}
.mode-btn.rad {
    color: var(--accent-teal);
    border-color: rgba(56,217,192,0.2);
}

/* ── 2nd Button ─── */
.second-btn {
    font-family: var(--font-display);
    font-size: 0.72rem;
    letter-spacing: 0.06em;
    color: var(--text-secondary);
}
.second-btn.active {
    background: rgba(247,201,72,0.15) !important;
    color: var(--accent-yellow) !important;
    border-color: rgba(247,201,72,0.4) !important;
    box-shadow: 0 0 14px rgba(247,201,72,0.15) !important;
}

/* ── Control Buttons (AC / DEL) ──────────────── */
.control-btn {
    font-family: var(--font-display);
}

.ac-btn {
    background: rgba(247, 95, 95, 0.15);
    color: var(--accent-red);
    border-color: rgba(247,95,95,0.25);
    font-size: 0.82rem;
    letter-spacing: 0.06em;
    font-weight: 700;
}
.ac-btn:hover {
    background: rgba(247,95,95,0.25);
    border-color: rgba(247,95,95,0.45);
    box-shadow: 0 0 14px rgba(247,95,95,0.12);
}

.del-btn {
    background: rgba(247, 95, 95, 0.08);
    color: var(--accent-red);
    border-color: rgba(247,95,95,0.15);
    font-size: 1rem;
}
.del-btn:hover {
    background: rgba(247,95,95,0.18);
    border-color: rgba(247,95,95,0.35);
}

/* ── Equals Button */
.equals-btn {
    grid-column: span 2;
    background: var(--accent-blue);
    color: #fff;
    font-family: var(--font-display);
    font-size: 1.3rem;
    font-weight: 700;
    border: none;
    box-shadow: 0 4px 20px rgba(79,142,247,0.35);
    letter-spacing: 0.05em;
}
.equals-btn:hover {
    background: var(--accent-blue-h);
    box-shadow: 0 4px 28px rgba(79,142,247,0.5);
    transform: translateY(-1px);
}
.equals-btn:active {
    transform: scale(0.93) translateY(0);
}

/* ── 2nd mode: sci buttons light up yellow ───── */
.second-active .sci-btn {
    color: var(--accent-yellow);
    border-color: rgba(247,201,72,0.18);
}

/* ── Keyboard Hint*/
.keyboard-hint {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 4px;
    opacity: 0.4;
    font-size: 0.65rem;
    color: var(--text-secondary);
    letter-spacing: 0.06em;
}
.hint-keys {
    font-family: var(--font-display);
    font-size: 0.6rem;
    color: var(--text-dim);
}

/* ── Button press flash animation ───────────── */
@keyframes btn-flash {
    0%   { box-shadow: 0 0 0 0 rgba(79,142,247,0.4); }
    100% { box-shadow: 0 0 0 8px rgba(79,142,247,0); }
}
.btn.flash { animation: btn-flash 0.25s ease-out; }

/* ── Responsive ─── */
@media (max-width: 520px) {
    :root { --btn-size: 48px; --gap: 5px; }
    .calculator-grid { padding: 10px; }
    .current-operand { font-size: 2rem; }
    .sci-btn  { font-size: 0.7rem; }
    .top-btn  { font-size: 0.72rem; }
    .calc-brand { font-size: 0.75rem; }
    .num-grid { grid-template-rows: repeat(4, 48px); }}

@media (max-width: 380px) {
    :root { --btn-size: 42px; --gap: 4px; }
    .current-operand { font-size: 1.7rem; }
    .sci-btn  { font-size: 0.6rem; }
    .top-btn  { font-size: 0.65rem; }
    .calculator-grid { padding: 8px; }
    .num-grid { grid-template-rows: repeat(4, 42px); }}

@media (max-height: 700px) {
    :root { --btn-size: 46px; }
    .display { min-height: 90px; }
    .num-grid { grid-template-rows: repeat(4, 46px); }}