* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --bg-primary: #f5f7fa;
    --bg-secondary: #ffffff;
    --bg-calc: #ffffff;
    --text-primary: #1a1a2e;
    --text-secondary: #555;
    --border-color: #e0e0e0;
    --shadow: 0 8px 32px rgba(0,0,0,0.08);
    --accent: #6c63ff;
    --accent-hover: #5a52d5;
    --btn-num-bg: #f0f0f5;
    --btn-op-bg: #e8e8ff;
    --btn-eq-bg: #6c63ff;
    --btn-eq-text: #fff;
    --history-bg: #fafafa;
    --hover-bg: #e8e8ff;
    --footer-bg: #1a1a2e;
    --footer-text: #ccc;
    --danger: #ff4757;
    --success: #2ed573;
}

[data-theme="dark"] {
    --bg-primary: #0f0f1a;
    --bg-secondary: #1a1a2e;
    --bg-calc: #16213e;
    --text-primary: #eaeaea;
    --text-secondary: #aaa;
    --border-color: #2a2a4a;
    --shadow: 0 8px 32px rgba(0,0,0,0.4);
    --accent: #7c7aff;
    --accent-hover: #6a68e0;
    --btn-num-bg: #2a2a4a;
    --btn-op-bg: #3a3a6a;
    --btn-eq-bg: #7c7aff;
    --btn-eq-text: #fff;
    --history-bg: #1a1a2e;
    --hover-bg: #3a3a6a;
    --footer-bg: #0a0a15;
    --footer-text: #888;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    transition: background 0.3s, color 0.3s;
}

/* 导航栏 */
.navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 30px;
    background: var(--bg-secondary);
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
    position: sticky;
    top: 0;
    z-index: 1000;
}

.nav-brand .logo {
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--accent);
    text-decoration: none;
}

.nav-links {
    display: flex;
    list-style: none;
    align-items: center;
    gap: 20px;
}

.nav-links li a {
    text-decoration: none;
    color: var(--text-primary);
    font-weight: 500;
    padding: 8px 12px;
    border-radius: 8px;
    transition: background 0.3s, color 0.3s;
}

.nav-links li a:hover,
.nav-links li a.active {
    background: var(--hover-bg);
    color: var(--accent);
}

.theme-btn {
    background: none;
    border: 2px solid var(--border-color);
    font-size: 1.4rem;
    cursor: pointer;
    padding: 6px 12px;
    border-radius: 50%;
    transition: 0.3s;
}

.theme-btn:hover {
    background: var(--hover-bg);
}

.hamburger {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 5px;
}

.hamburger span {
    width: 28px;
    height: 3px;
    background: var(--text-primary);
    border-radius: 3px;
    transition: 0.3s;
}

/* Hero */
.hero {
    text-align: center;
    padding: 40px 20px 20px;
    background: linear-gradient(135deg, var(--accent) 0%, #8b7aff 100%);
    color: #fff;
}

.hero h1 {
    font-size: 2rem;
    margin-bottom: 10px;
    font-weight: 700;
}

.hero p {
    font-size: 1.1rem;
    opacity: 0.9;
}

/* 计算器区域 */
.calculator-section {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 30px;
    padding: 30px 20px;
    flex: 1;
}

.calc-container {
    background: var(--bg-calc);
    border-radius: 24px;
    box-shadow: var(--shadow);
    padding: 25px;
    width: 100%;
    max-width: 480px;
    transition: background 0.3s;
}

.display-area {
    background: var(--btn-num-bg);
    border-radius: 16px;
    padding: 20px;
    margin-bottom: 15px;
    min-height: 100px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: flex-end;
    word-break: break-all;
}

.expression {
    font-size: 1rem;
    color: var(--text-secondary);
    min-height: 24px;
}

.result {
    font-size: 2.4rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-top: 5px;
}

.toolbar {
    display: flex;
    gap: 10px;
    margin-bottom: 15px;
    flex-wrap: wrap;
}

.tool-btn {
    padding: 10px 16px;
    border: none;
    border-radius: 12px;
    background: var(--btn-op-bg);
    color: var(--text-primary);
    font-weight: 600;
    cursor: pointer;
    transition: 0.3s;
    flex: 1;
    min-width: 50px;
}

.tool-btn:hover {
    background: var(--accent);
    color: #fff;
}

.sci-buttons {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 8px;
    margin-bottom: 15px;
}

.sci-btn {
    padding: 10px 4px;
    border: none;
    border-radius: 10px;
    background: var(--btn-op-bg);
    color: var(--text-primary);
    font-weight: 600;
    font-size: 0.85rem;
    cursor: pointer;
    transition: 0.3s;
}

.sci-btn:hover {
    background: var(--accent);
    color: #fff;
}

.basic-buttons {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 8px;
}

.btn {
    padding: 16px 8px;
    border: none;
    border-radius: 12px;
    font-size: 1.2rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
    user-select: none;
}

.btn:active {
    transform: scale(0.95);
}

.btn-num {
    background: var(--btn-num-bg);
    color: var(--text-primary);
}

.btn-num:hover {
    background: var(--hover-bg);
}

.btn-op {
    background: var(--btn-op-bg);
    color: var(--accent);
}

.btn-op:hover {
    background: var(--accent);
    color: #fff;
}

.btn-eq {
    background: var(--btn-eq-bg);
    color: var(--btn-eq-text);
}

.btn-eq:hover {
    background: var(--accent-hover);
}

.btn-mem {
    background: var(--btn-num-bg);
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.btn-mem:hover {
    background: var(--hover-bg);
}

/* 历史记录 */
.history-panel {
    background: var(--bg-calc);
    border-radius: 24px;
    box-shadow: var(--shadow);
    padding: 25px;
    width: 100%;
    max-width: 320px;
    max-height: 600px;
    overflow-y: auto;
    transition: background 0.3s;
}

.history-panel h2 {
    font-size: 1.2rem;
    margin-bottom: 15px;
    color: var(--text-primary);
}

.history-list {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.history-item {
    background: var(--history-bg);
    padding: 12px 16px;
    border-radius: 12px;
    cursor: pointer;
    transition: 0.3s;
    border: 1px solid var(--border-color);
}

.history-item:hover {
    background: var(--hover-bg);
    transform: translateX(4px);
}

.h-expr {
    display: block;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.h-result {
    display: block;
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--accent);
}

.no-history {
    color: var(--text-secondary);
    text-align: center;
    padding: 20px;
}

/* 管理后台 */
.admin-section {
    display: flex;
    justify-content: center;
    align-items: flex-start;
    padding: 40px 20px;
    flex: 1;
}

.login-box, .admin-panel {
    background: var(--bg-calc);
    border-radius: 24px;
    box-shadow: var(--shadow);
    padding: 40px;
    width: 100%;
    max-width: 500px;
}

.login-box h2, .admin-panel h2 {
    margin-bottom: 20px;
    color: var(--text-primary);
}

.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 6px;
    font-weight: 500;
    color: var(--text-primary);
}

.form-group input {
    width: 100%;
    padding: 12px 16px;
    border: 2px solid var(--border-color);
    border-radius: 12px;
    background: var(--bg-primary);
    color: var(--text-primary);
    font-size: 1rem;
    transition: border 0.3s;
}

.form-group input:focus {
    border-color: var(--accent);
    outline: none;
}

.btn-primary {
    width: 100%;
    padding: 14px;
    border: none;
    border-radius: 12px;
    background: var(--accent);
    color: #fff;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: 0.3s;
}

.btn-primary:hover {
    background: var(--accent-hover);
}

.btn-danger {
    padding: 12px 24px;
    border: none;
    border-radius: 12px;
    background: var(--danger);
    color: #fff;
    font-weight: 600;
    cursor: pointer;
    transition: 0.3s;
}

.btn-danger:hover {
    opacity: 0.9;
}

.error-msg {
    color: var(--danger);
    margin-bottom: 15px;
    font-weight: 500;
}

.logout-btn {
    background: none;
    border: 2px solid var(--danger);
    color: var(--danger);
    padding: 6px 16px;
    border-radius: 8px;
    cursor: pointer;
    font-weight: 600;
    transition: 0.3s;
}

.logout-btn:hover {
    background: var(--danger);
    color: #fff;
}

.history-table-wrapper {
    overflow-x: auto;
    margin-top: 20px;
}

.history-table {
    width: 100%;
    border-collapse: collapse;
}

.history-table th, .history-table td {
    padding: 12px 16px;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

.history-table th {
    background: var(--btn-num-bg);
    font-weight: 600;
    color: var(--text-primary);
}

.history-table tr:hover {
    background: var(--hover-bg);
}

.admin-actions {
    margin-bottom: 20px;
}

/* 页脚 */
footer {
    background: var(--footer-bg);
    color: var(--footer-text);
    padding: 20px;
    text-align: center;
    margin-top: auto;
}

.footer-content a {
    color: var(--accent);
    text-decoration: none;
    margin: 0 8px;
}

.footer-content a:hover {
    text-decoration: underline;
}

/* 响应式 */
@media (max-width: 768px) {
    .navbar {
        padding: 12px 16px;
    }

    .nav-links {
        display: none;
        flex-direction: column;
        position: absolute;
        top: 60px;
        left: 0;
        right: 0;
        background: var(--bg-secondary);
        padding: 20px;
        box-shadow: 0 8px 20px rgba(0,0,0,0.1);
        gap: 10px;
    }

    .nav-links.active {
        display: flex;
    }

    .hamburger {
        display: flex;
    }

    .hero h1 {
        font-size: 1.4rem;
    }

    .calculator-section {
        flex-direction: column;
        align-items: center;
        padding: 20px 12px;
    }

    .calc-container, .history-panel {
        max-width: 100%;
    }

    .sci-buttons {
        grid-template-columns: repeat(4, 1fr);
    }

    .basic-buttons {
        grid-template-columns: repeat(4, 1fr);
    }

    .btn {
        padding: 14px 6px;
        font-size: 1rem;
    }

    .result {
        font-size: 1.8rem;
    }
}

@media (max-width: 480px) {
    .sci-buttons {
        grid-template-columns: repeat(3, 1fr);
    }

    .basic-buttons {
        grid-template-columns: repeat(4, 1fr);
    }

    .btn {
        padding: 12px 4px;
        font-size: 0.9rem;
    }

    .display-area {
        padding: 14px;
        min-height: 80px;
    }
}