/* ======= Reset & Variables ======= */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    --bg: #0f172a;
    --wrapper-bg: #1e293b;
    --display-bg: #0f172a;
    --text: #f1f5f9;
    --text-muted: #94a3b8;
    --num-bg: #334155;
    --num-hover: #475569;
    --op-bg: #6366f1;
    --op-hover: #4f46e5;
    --fn-bg: #1e293b;
    --fn-hover: #334155;
    --eq-bg: #22c55e;
    --eq-hover: #16a34a;
    --border: #334155;
    --shadow: rgba(0, 0, 0, 0.5);
}

[data-theme="light"] {
    --bg: #e2e8f0;
    --wrapper-bg: #ffffff;
    --display-bg: #f1f5f9;
    --text: #0f172a;
    --text-muted: #64748b;
    --num-bg: #e2e8f0;
    --num-hover: #cbd5e1;
    --op-bg: #6366f1;
    --op-hover: #4f46e5;
    --fn-bg: #f1f5f9;
    --fn-hover: #e2e8f0;
    --eq-bg: #22c55e;
    --eq-hover: #16a34a;
    --border: #cbd5e1;
    --shadow: rgba(0, 0, 0, 0.1);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background: var(--bg);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 16px;
    transition: background 0.3s;
}

/* ======= Wrapper ======= */
.calc-wrapper {
    width: 100%;
    max-width: 380px;
}

.top-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
    padding: 0 4px;
}

.logo {
    color: var(--text);
    font-size: 1.3rem;
    font-weight: 700;
    transition: color 0.3s;
}
.logo span {
    color: var(--op-bg);
}

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

.icon-btn {
    background: var(--fn-bg);
    border: 1px solid var(--border);
    color: var(--text);
    font-size: 1.1rem;
    width: 38px;
    height: 38px;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
}
.icon-btn:hover {
    background: var(--fn-hover);
    transform: scale(1.05);
}

/* ======= Calculator ======= */
.calculator {
    background: var(--wrapper-bg);
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 20px 60px var(--shadow);
    transition: background 0.3s, box-shadow 0.3s;
}

/* ======= Display ======= */
.display {
    background: var(--display-bg);
    border-radius: 14px;
    padding: 20px;
    min-height: 100px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: flex-end;
    margin-bottom: 16px;
    overflow: hidden;
    transition: background 0.3s;
}

.expression {
    color: var(--text-muted);
    font-size: 0.95rem;
    min-height: 1.3em;
    word-break: break-all;
    text-align: right;
    width: 100%;
    transition: color 0.3s;
}

.result {
    color: var(--text);
    font-size: 2.6rem;
    font-weight: 700;
    word-break: break-all;
    text-align: right;
    width: 100%;
    line-height: 1.2;
    transition: color 0.3s, transform 0.15s;
}
.result.pop {
    animation: popIn 0.18s ease;
}
@keyframes popIn {
    0%   { transform: scale(1); }
    50%  { transform: scale(1.06); }
    100% { transform: scale(1); }
}

/* ======= Buttons Grid ======= */
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.btn {
    padding: 18px 0;
    font-size: 1.25rem;
    font-weight: 600;
    border: none;
    border-radius: 14px;
    cursor: pointer;
    transition: all 0.15s;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
    position: relative;
    overflow: hidden;
}

/* Ripple */
.btn::after {
    content: "";
    position: absolute;
    inset: 0;
    background: radial-gradient(circle, rgba(255,255,255,0.3) 10%, transparent 70%);
    opacity: 0;
    transform: scale(0);
    border-radius: inherit;
}
.btn.ripple::after {
    animation: rippleAnim 0.5s ease-out;
}
@keyframes rippleAnim {
    0%   { opacity: 1; transform: scale(0); }
    100% { opacity: 0; transform: scale(2.5); }
}

.btn:active {
    transform: scale(0.93);
}

/* Number buttons */
.btn.num {
    background: var(--num-bg);
    color: var(--text);
}
.btn.num:hover { background: var(--num-hover); }

/* Operator buttons */
.btn.op {
    background: var(--op-bg);
    color: #fff;
}
.btn.op:hover { background: var(--op-hover); }

/* Function buttons */
.btn.fn {
    background: var(--fn-bg);
    color: var(--text);
    border: 1px solid var(--border);
}
.btn.fn:hover { background: var(--fn-hover); }

/* Equals */
.btn.eq {
    background: var(--eq-bg);
    color: #fff;
}
.btn.eq:hover { background: var(--eq-hover); }

/* Zero spans two cols */
.btn.zero {
    grid-column: span 2;
}

/* ======= Hint ======= */
.hint {
    text-align: center;
    color: var(--text-muted);
    font-size: 0.8rem;
    margin-top: 12px;
    transition: color 0.3s;
}

/* ======= Responsive ======= */
@media (max-width: 400px) {
    .calculator { padding: 14px; }
    .btn { padding: 15px 0; font-size: 1.1rem; border-radius: 12px; }
    .result { font-size: 2.2rem; }
    .display { padding: 16px; min-height: 85px; }
}
@media (max-width: 340px) {
    .buttons { gap: 6px; }
    .btn { padding: 13px 0; font-size: 1rem; }
}