:root {
    color-scheme: light;
    --bg: #f3f6fb;
    --panel: rgba(255, 255, 255, 0.94);
    --panel-strong: #ffffff;
    --text: #172033;
    --muted: #758198;
    --line: #e4e9f2;
    --key: #f1f4f9;
    --key-hover: #e7ecf5;
    --primary: #5b5ce2;
    --primary-soft: #ececff;
    --danger: #d94b64;
    --danger-soft: #fff0f3;
    --shadow: 0 24px 70px rgba(45, 56, 91, 0.12);
}

body.dark {
    color-scheme: dark;
    --bg: #10131a;
    --panel: rgba(25, 30, 41, 0.96);
    --panel-strong: #1b202c;
    --text: #eef2fb;
    --muted: #99a4b8;
    --line: #303746;
    --key: #252c39;
    --key-hover: #303849;
    --primary: #8f90ff;
    --primary-soft: #282956;
    --danger: #ff7a91;
    --danger-soft: #3a222b;
    --shadow: 0 24px 70px rgba(0, 0, 0, 0.28);
}

* { box-sizing: border-box; }

body {
    margin: 0;
    min-height: 100vh;
    font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "Microsoft YaHei", sans-serif;
    background:
        radial-gradient(circle at 10% 10%, rgba(91, 92, 226, 0.12), transparent 28rem),
        var(--bg);
    color: var(--text);
    transition: background 0.2s ease, color 0.2s ease;
}

button, input { font: inherit; }
button { -webkit-tap-highlight-color: transparent; }

.page-shell {
    width: min(1120px, calc(100% - 32px));
    margin: 0 auto;
    padding: 54px 0 60px;
}

.topbar {
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
    gap: 24px;
    margin-bottom: 26px;
}

.eyebrow {
    display: inline-block;
    color: var(--primary);
    font-size: 12px;
    font-weight: 800;
    letter-spacing: 0.16em;
}

h1, h2, p { margin-top: 0; }
h1 { margin: 5px 0 5px; font-size: clamp(34px, 6vw, 58px); letter-spacing: -0.055em; }
h2 { margin: 5px 0 4px; font-size: 25px; letter-spacing: -0.035em; }
.topbar p, .history-header p { color: var(--muted); margin-bottom: 0; }

.workspace {
    display: grid;
    grid-template-columns: minmax(330px, 0.86fr) minmax(360px, 1.14fr);
    gap: 24px;
}

.calculator-card, .history-card {
    border: 1px solid var(--line);
    background: var(--panel);
    border-radius: 26px;
    box-shadow: var(--shadow);
    backdrop-filter: blur(12px);
}

.calculator-card { padding: 28px; }
.history-card { padding: 28px; min-height: 610px; }

.display-wrap label { color: var(--muted); font-size: 13px; font-weight: 700; }
.display {
    width: 100%;
    height: 84px;
    margin-top: 10px;
    padding: 0 18px;
    border: 1px solid var(--line);
    border-radius: 18px;
    outline: none;
    background: var(--panel-strong);
    color: var(--text);
    text-align: right;
    font-size: clamp(25px, 5vw, 36px);
    font-weight: 650;
    letter-spacing: -0.035em;
}
.display:focus { border-color: var(--primary); box-shadow: 0 0 0 4px rgba(91, 92, 226, 0.10); }

.status-row {
    min-height: 38px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px;
    padding: 9px 2px 3px;
    font-size: 13px;
}
.message { color: var(--danger); font-weight: 700; }
.message.success { color: #248a5c; }
.backend-status { color: var(--muted); white-space: nowrap; }
.backend-status.online { color: #248a5c; }
.backend-status.offline { color: var(--danger); }

.button-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    margin-top: 10px;
}
.button-grid button {
    min-height: 62px;
    border: 0;
    border-radius: 16px;
    background: var(--key);
    color: var(--text);
    font-size: 20px;
    font-weight: 750;
    cursor: pointer;
    transition: transform .12s ease, background .12s ease;
}
.button-grid button:hover { transform: translateY(-2px); background: var(--key-hover); }
.button-grid button:active { transform: translateY(0); }
.button-grid .operator { background: var(--primary-soft); color: var(--primary); }
.button-grid .equal { background: var(--primary); color: white; }
.button-grid .danger { background: var(--danger-soft); color: var(--danger); }
.hint { margin: 18px 0 0; color: var(--muted); text-align: center; font-size: 13px; }

.history-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
    padding-bottom: 20px;
    border-bottom: 1px solid var(--line);
}
.history-actions { display: flex; gap: 8px; }
.ghost-button, .danger-outline {
    border: 1px solid var(--line);
    border-radius: 12px;
    padding: 10px 13px;
    background: var(--panel-strong);
    color: var(--text);
    cursor: pointer;
}
.danger-outline { border-color: rgba(217, 75, 100, .32); color: var(--danger); }

.history-list {
    max-height: 485px;
    overflow: auto;
    padding: 15px 3px 3px 0;
}
.history-item {
    display: grid;
    grid-template-columns: minmax(0, 1fr) auto;
    gap: 16px;
    align-items: center;
    margin-bottom: 10px;
    padding: 15px 14px 15px 16px;
    border: 1px solid var(--line);
    border-radius: 16px;
    background: var(--panel-strong);
}
.history-expression { font-weight: 750; word-break: break-all; }
.history-result { margin-top: 5px; color: var(--primary); font-size: 18px; font-weight: 800; }
.history-time { margin-top: 5px; color: var(--muted); font-size: 12px; }
.delete-button {
    border: 0;
    border-radius: 10px;
    padding: 8px 11px;
    background: var(--danger-soft);
    color: var(--danger);
    font-weight: 700;
    cursor: pointer;
}
.empty, .loading {
    color: var(--muted);
    text-align: center;
    padding: 70px 16px;
}

@media (max-width: 820px) {
    .page-shell { padding-top: 28px; }
    .workspace { grid-template-columns: 1fr; }
    .history-card { min-height: auto; }
    .history-list { max-height: none; }
}

@media (max-width: 520px) {
    .page-shell { width: min(100% - 20px, 1120px); }
    .topbar { align-items: center; }
    .calculator-card, .history-card { padding: 19px; border-radius: 21px; }
    .history-header { align-items: flex-start; flex-direction: column; }
    .button-grid button { min-height: 56px; }
}