:root {
    --primary-color: #0b0d12;
    --primary-light: #f4f5f7;
    --secondary-color: #4b5563;
    --accent-color: #3b82f6;
    --success-color: #0f766e;
    --warning-color: #b45309;
    --danger-color: #b91c1c;
    --text-color: #111827;
    --text-light: #6b7280;
    --border-color: #e5e7eb;
    --bg-color: #f8f9fb;
    --bg-card: #ffffff;
    --shadow: 0 1px 2px rgba(15, 23, 42, 0.08);
    --shadow-lg: 0 12px 28px rgba(15, 23, 42, 0.18);
    --border-radius: 8px;
    --font-sans: 'Helvetica Neue', 'Avenir Next', 'Univers', 'Helvetica', system-ui, sans-serif;
    --font-mono: 'SF Mono', 'Menlo', 'Monaco', monospace;
}

body[data-theme="dark"] {
    --primary-color: #f9fafb;
    --primary-light: #1f2937;
    --secondary-color: #9ca3af;
    --accent-color: #60a5fa;
    --success-color: #34d399;
    --warning-color: #fbbf24;
    --danger-color: #f87171;
    --text-color: #f9fafb;
    --text-light: #9ca3af;
    --border-color: #374151;
    --bg-color: #121212;
    --bg-card: #1e1e1e;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.45);
    --shadow-lg: 0 16px 32px rgba(0, 0, 0, 0.55);
}

@media (prefers-color-scheme: dark) {
    body[data-theme="system"] {
        --primary-color: #f9fafb;
        --primary-light: #1f2937;
        --secondary-color: #9ca3af;
        --accent-color: #60a5fa;
        --success-color: #34d399;
        --warning-color: #fbbf24;
        --danger-color: #f87171;
        --text-color: #f9fafb;
        --text-light: #9ca3af;
        --border-color: #374151;
        --bg-color: #121212;
        --bg-card: #1e1e1e;
        --shadow: 0 1px 2px rgba(0, 0, 0, 0.45);
        --shadow-lg: 0 16px 32px rgba(0, 0, 0, 0.55);
    }
}

* { box-sizing: border-box; }

body {
    font-family: var(--font-sans);
    background-color: var(--bg-color);
    color: var(--text-color);
    margin: 0;
    line-height: 1.6;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    transition: background-color 0.2s ease, color 0.2s ease;
}

.container {
    width: 92%;
    max-width: 1400px;
    margin: 0 auto;
    padding: 24px 0;
}

main.container {
    flex-grow: 1;
}

/* =================================================================
   HEADER & FOOTER
   ================================================================= */

.navbar { background-color: var(--bg-card); border-bottom: 1px solid var(--border-color); padding: 0 4%; }
.nav-container { display: flex; justify-content: space-between; align-items: center; height: 64px; max-width: 1400px; margin: 0 auto; }
.nav-brand { font-size: 1.25rem; font-weight: 600; color: var(--text-color); text-decoration: none; }
.nav-actions { display: flex; align-items: center; gap: 12px; }
.settings-button {
    border: 1px solid var(--border-color);
    background: var(--bg-card);
    color: var(--text-color);
    font-weight: 600;
    font-size: 0.85rem;
    padding: 8px 14px;
    border-radius: 999px;
    cursor: pointer;
    transition: background-color 0.15s ease;
}
.settings-button:hover { background: var(--primary-light); }

.footer {
    text-align: center;
    padding: 20px 0;
    color: var(--text-light);
    font-size: 0.9rem;
    margin-top: 30px;
    border-top: 1px solid var(--border-color);
}

/* =================================================================
   SETTINGS PANEL
   ================================================================= */
.settings-overlay {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.2);
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.2s ease, visibility 0.2s ease;
    z-index: 1000;
}
.settings-overlay.open { opacity: 1; visibility: visible; }
.settings-panel {
    position: fixed;
    top: 0;
    right: 0;
    width: 360px;
    height: 100vh;
    background: var(--bg-card);
    border-left: 1px solid var(--border-color);
    box-shadow: var(--shadow-lg);
    transform: translateX(100%);
    transition: transform 0.25s ease;
    z-index: 1001;
    display: flex;
    flex-direction: column;
}
.settings-panel.open { transform: translateX(0); }
.settings-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 18px 24px;
    border-bottom: 1px solid var(--border-color);
}
.settings-header h3 { margin: 0; font-size: 1.1rem; }
.settings-close {
    background: none;
    border: none;
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-light);
    cursor: pointer;
}
.settings-content { padding: 20px 24px; overflow-y: auto; flex: 1; }
.settings-section { margin-bottom: 24px; }
.settings-section h4 { margin-bottom: 14px; font-size: 0.95rem; color: var(--secondary-color); }
.setting-row { display: flex; align-items: center; justify-content: space-between; gap: 14px; margin-bottom: 16px; }
.setting-label { font-weight: 600; font-size: 0.9rem; color: var(--text-color); }
.setting-help { font-size: 0.8rem; color: var(--text-light); margin-top: 2px; }
.settings-footer { padding: 18px 24px; border-top: 1px solid var(--border-color); }
.btn-secondary { background-color: transparent; color: var(--text-color); border: 1px solid var(--border-color); padding: 8px 14px; border-radius: var(--border-radius); font-weight: 600; cursor: pointer;}
.btn-secondary:hover { background-color: var(--primary-light); }

.segmented {
    display: inline-flex;
    gap: 4px;
    background: var(--primary-light);
    border: 1px solid var(--border-color);
    border-radius: 999px;
    padding: 4px;
}
.segmented button {
    border: none;
    background: transparent;
    color: var(--text-light);
    font-size: 0.8rem;
    font-weight: 600;
    padding: 6px 10px;
    border-radius: 999px;
    cursor: pointer;
    transition: all 0.15s ease;
}
.segmented button:hover { color: var(--text-color); }
.segmented button.active {
    background: var(--accent-color);
    color: var(--bg-card) !important;
}


/* =================================================================
   MAIN TOOL STYLES
   ================================================================= */

.tool-header {
    text-align: center;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 15px;
    margin-bottom: 20px;
}
.tool-header h1 { margin-bottom: 0.25rem; }
.tool-header p {
    color: var(--text-light);
    margin-top: 5px;
    max-width: 60ch;
    margin-left: auto;
    margin-right: auto;
}

.tool-layout {
    display: grid;
    grid-template-columns: minmax(320px, 1fr) 2fr;
    gap: 28px;
    align-items: start;
}

.card {
    background-color: var(--bg-card);
    border-radius: var(--border-radius);
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow);
    padding: 24px;
}

.tool-inputs h2, .tool-outputs h2 {
    margin-top: 0;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 10px;
    margin-bottom: 20px;
}

.tabs {
    display: flex;
    border-bottom: 1px solid var(--border-color);
    margin-bottom: 24px;
}
.tab-link {
    padding: 10px 16px;
    cursor: pointer;
    background: none;
    border: none;
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-light);
    border-bottom: 3px solid transparent;
    margin-bottom: -1px;
    transition: color 0.2s ease, border-color 0.2s ease;
}
.tab-link:hover { color: var(--text-color); }
.tab-link.active {
    color: var(--accent-color);
    border-bottom-color: var(--accent-color);
}
.tab-content { display: none; }
.tab-content.active { display: block; animation: fadeIn 0.5s; }

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

.theory-section {
    margin-bottom: 32px;
}
.theory-section h3 {
    font-size: 1.5rem;
    border-bottom: 2px solid var(--accent-color);
    padding-bottom: 8px;
    margin-bottom: 16px;
}
.theory-section h4 {
    font-size: 1.2rem;
    margin-top: 24px;
    margin-bottom: 12px;
    color: var(--secondary-color);
}
.theory-section p, .theory-section ul {
    max-width: 80ch;
    color: var(--text-light);
}
.theory-section ul {
    padding-left: 20px;
}

.equation-card {
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 16px 20px;
    margin: 16px 0;
    overflow-x: auto;
}
.equation-card strong {
    display: block;
    margin-bottom: 8px;
    color: var(--secondary-color);
    font-size: 0.9rem;
}
.equation-card .equation-expression {
    font-size: 1.1rem;
}

.control-group {
    margin-bottom: 20px;
}
.control-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 500;
    color: var(--text-light);
}
.control-group input[type="range"] {
    width: 100%;
    cursor: pointer;
}

.results-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin-top: 24px;
    padding-top: 24px;
    border-top: 1px solid var(--border-color);
}
.result-item {
    background: var(--bg-color);
    padding: 16px;
    border-radius: var(--border-radius);
    text-align: center;
}
.result-item .label {
    font-size: 0.8rem;
    color: var(--text-light);
    margin-bottom: 6px;
}
.result-item .value {
    font-size: 1.5rem;
    font-weight: 600;
    font-family: var(--font-mono);
    color: var(--accent-color);
}

.plot-container {
    width: 100%;
    height: 300px;
    margin-bottom: 20px;
}
.plot-container:last-child {
    margin-bottom: 0;
}

.footer {
    text-align: center;
    padding: 20px 0;
    color: var(--text-light);
    font-size: 0.9rem;
    margin-top: 30px;
}

@media (max-width: 900px) {
    .tool-layout {
        grid-template-columns: 1fr;
    }
}