/* ============================================
   Stress-Strain Curve Analyzer - Premium CSS
   ============================================ */

html {
    scrollbar-gutter: stable;
}

/* Page Layout */
:root {
    --color-elastic-bg: rgba(59, 130, 246, 0.05);
    --color-plastic-bg: rgba(239, 68, 68, 0.03);
}

.curve-app {
    min-height: 100vh;
    background: var(--color-bg-primary);
}

.curve-app-header {
    background: rgba(255, 255, 255, 0.85);
    backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--color-border);
    padding: 0.75rem 1.5rem;
    position: sticky;
    top: 0;
    z-index: 100;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.curve-app-header .back-link {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--color-text-secondary);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.9rem;
    transition: all 0.2s ease;
    padding: 0.5rem 1rem;
    border-radius: 8px;
}

.curve-app-header .back-link:hover {
    color: var(--color-accent);
    background: var(--color-bg-tertiary);
}

.curve-app-header .back-link svg {
    width: 18px;
    height: 18px;
    transition: transform 0.2s ease;
}

.curve-app-header .back-link:hover svg {
    transform: translateX(-3px);
}

.curve-app-title {
    font-family: var(--font-heading);
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--color-text-primary);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.curve-app-title .title-icon {
    font-size: 1.3rem;
}

.curve-app-actions {
    display: flex;
    gap: 0.5rem;
}

/* Theme Toggle styles */
.icon-button {
    background: transparent;
    border: none;
    cursor: pointer;
    font-size: 1.2rem;
    padding: 0.5rem;
    border-radius: 50%;
    transition: background-color 0.2s ease;
    display: flex;
    align-items: center;
    justify-content: center;
}

.icon-button:hover {
    background: var(--color-bg-tertiary);
}

.theme-icon {
    width: 20px;
    height: 20px;
}

/* Main Layout Container */
.curve-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1.2rem;
    width: 100%;
}

/* Accordion Toggle Button */
.accordion-toggle-btn {
    width: 100%;
    padding: 1rem 1.5rem;
    background: var(--color-bg-secondary);
    border: 1.5px solid var(--color-border);
    border-radius: 10px;
    color: var(--color-text-primary);
    font-family: var(--font-heading);
    font-weight: 700;
    font-size: 0.95rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: space-between;
    box-shadow: var(--shadow-sm);
    transition: all 0.2s ease;
    outline: none;
}
.accordion-toggle-btn:hover {
    border-color: var(--color-accent);
    background: var(--color-bg-tertiary);
    color: var(--color-accent);
}
.accordion-toggle-btn .chevron {
    transition: transform 0.3s ease;
    font-size: 0.8rem;
    color: var(--color-text-muted);
}
.accordion-toggle-btn.active .chevron {
    transform: rotate(180deg);
    color: var(--color-accent);
}

/* Collapsible Accordion Content */
.accordion-content {
    max-height: 0;
    opacity: 0;
    overflow: hidden;
    transition: max-height 0.4s cubic-bezier(0.4, 0, 0.2, 1), opacity 0.3s ease;
    width: 100%;
}
.accordion-content.expanded {
    max-height: 2500px; /* Safe upper limit for accordion height */
    opacity: 1;
    margin-top: 0.5rem;
}

.panel-section {
    padding: 0.85rem 1.15rem;
    border-bottom: 1px solid var(--color-border-light);
}

.panel-section:last-child {
    border-bottom: none;
}

.panel-section-title {
    font-family: var(--font-heading);
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--color-text-muted);
    margin-bottom: 0.75rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.panel-section-title .section-icon {
    font-size: 0.95rem;
}

/* Presets Grid */
.preset-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0.5rem;
}

.preset-btn {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    padding: 0.45rem 0.6rem;
    background: var(--color-bg-tertiary);
    border: 1.5px solid var(--color-border-light);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
    text-align: left;
    gap: 0.15rem;
}

.preset-btn:hover {
    border-color: var(--color-accent);
    background: var(--color-bg-secondary);
    transform: translateY(-1px);
}

.preset-btn.active {
    border-color: var(--color-accent);
    background: rgba(220, 38, 38, 0.05);
    box-shadow: 0 0 0 3px rgba(220, 38, 38, 0.1);
}

.preset-name {
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--color-text-primary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    width: 100%;
}

.preset-type {
    font-size: 0.68rem;
    color: var(--color-text-muted);
}

/* Form Properties */
.prop-row {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
}

.prop-group {
    flex: 1;
}

.prop-group.full-width {
    width: 100%;
}

.prop-label {
    display: block;
    font-size: 0.74rem;
    font-weight: 600;
    color: var(--color-text-secondary);
    margin-bottom: 0.2rem;
}

.prop-input {
    width: 100%;
    padding: 0.4rem 0.55rem;
    background: var(--color-bg-tertiary);
    border: 1.5px solid var(--color-border);
    border-radius: 6px;
    color: var(--color-text-primary);
    font-family: var(--font-mono);
    font-size: 0.8rem;
    transition: all 0.2s ease;
}

.prop-input:focus {
    outline: none;
    border-color: var(--color-accent);
    box-shadow: 0 0 0 3px rgba(220, 38, 38, 0.1);
    background: var(--color-bg-secondary);
}

.prop-select {
    width: 100%;
    padding: 0.4rem 0.55rem;
    background: var(--color-bg-tertiary);
    border: 1.5px solid var(--color-border);
    border-radius: 6px;
    color: var(--color-text-primary);
    font-family: var(--font-body);
    font-size: 0.8rem;
    cursor: pointer;
    transition: all 0.2s ease;
}

.prop-select:focus {
    outline: none;
    border-color: var(--color-accent);
    box-shadow: 0 0 0 3px rgba(220, 38, 38, 0.1);
}

/* Switch styling */
.switch-group {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.5rem 0;
}

.switch-label {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--color-text-secondary);
}

.switch {
    position: relative;
    display: inline-block;
    width: 44px;
    height: 24px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--color-border);
    transition: .3s;
    border-radius: 24px;
}

.slider:before {
    position: absolute;
    content: "";
    height: 18px;
    width: 18px;
    left: 3px;
    bottom: 3px;
    background-color: white;
    transition: .3s;
    border-radius: 50%;
}

input:checked + .slider {
    background-color: var(--color-accent);
}

input:checked + .slider:before {
    transform: translateX(20px);
}

/* Comparison Button and List */
.action-btn {
    width: 100%;
    padding: 0.5rem;
    background: var(--color-bg-tertiary);
    border: 1.5px solid var(--color-border);
    border-radius: 8px;
    color: var(--color-text-primary);
    font-weight: 600;
    font-size: 0.8rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.4rem;
    transition: all 0.2s ease;
    margin-top: 0.4rem;
}

.action-btn:hover {
    background: var(--color-bg-secondary);
    border-color: var(--color-accent);
    color: var(--color-accent);
}

.action-btn.primary {
    background: var(--color-accent);
    border-color: var(--color-accent);
    color: white;
}

.action-btn.primary:hover {
    background: var(--color-accent-dark);
    border-color: var(--color-accent-dark);
    color: white;
}

.comparison-list {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
    margin-top: 0.6rem;
}

.comp-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.4rem 0.6rem;
    background: var(--color-bg-tertiary);
    border: 1px solid var(--color-border-light);
    border-radius: 6px;
    font-size: 0.76rem;
}

.comp-info {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    font-weight: 600;
}

.comp-color {
    width: 10px;
    height: 10px;
    border-radius: 50%;
}

.comp-remove {
    background: transparent;
    border: none;
    color: var(--color-text-muted);
    cursor: pointer;
    font-size: 0.9rem;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0.15rem;
    border-radius: 4px;
}

.comp-remove:hover {
    color: var(--color-accent);
    background: rgba(220, 38, 38, 0.05);
}

/* Validation Alert */
.validation-alert {
    background: rgba(220, 38, 38, 0.06);
    border: 1px solid rgba(220, 38, 38, 0.2);
    border-radius: 6px;
    padding: 0.6rem 0.85rem;
    color: var(--color-accent-dark);
    font-size: 0.78rem;
    margin-top: 0.6rem;
    display: none;
    animation: fadeIn 0.2s ease-out;
}

.validation-alert.active {
    display: block;
}

/* Results Grid */
.results-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0.5rem;
    margin-top: 0.4rem;
}

.result-card {
    background: var(--color-bg-tertiary);
    border: 1px solid var(--color-border-light);
    border-radius: 6px;
    padding: 0.45rem 0.6rem;
    display: flex;
    flex-direction: column;
    gap: 0.1rem;
}

.result-title {
    font-size: 0.68rem;
    font-weight: 600;
    text-transform: uppercase;
    color: var(--color-text-muted);
    letter-spacing: 0.05em;
}

.result-value {
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--color-text-primary);
    font-family: var(--font-mono);
}

.result-unit {
    font-size: 0.72rem;
    color: var(--color-text-muted);
    margin-left: 0.1rem;
}

/* Custom Container Heights & Paddings */

/* Status Bar */
.status-bar {
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border-light);
    padding: 0.45rem 1rem;
    border-radius: 8px;
    display: flex;
    align-items: center;
    gap: 0.6rem;
    font-size: 0.8rem;
    color: var(--color-text-secondary);
}

.status-dot {
    width: 7px;
    height: 7px;
    background: #10b981;
    border-radius: 50%;
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0% {
        box-shadow: 0 0 0 0 rgba(16, 185, 129, 0.4);
    }
    70% {
        box-shadow: 0 0 0 5px rgba(16, 185, 129, 0);
    }
    100% {
        box-shadow: 0 0 0 0 rgba(16, 185, 129, 0);
    }
}

.status-info {
    margin-left: auto;
    display: flex;
    gap: 0.75rem;
}

.status-info span {
    border-left: 1px solid var(--color-border);
    padding-left: 0.75rem;
}

.status-info span:first-child {
    border-left: none;
    padding-left: 0;
}

/* Diagram Container */
.diagram-container {
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: 10px;
    padding: 1rem;
    box-shadow: var(--shadow-sm);
    position: relative;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    height: 100%;
}

.diagram-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 0.75rem;
}

.diagram-title {
    font-family: var(--font-heading);
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--color-text-primary);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.diagram-title .dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
}

.diagram-title .dot.red { background: var(--color-accent); }

.diagram-svg-wrap {
    width: 100%;
    position: relative;
    cursor: crosshair;
    flex-grow: 1;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* SVG Chart Elements */
.chart-svg {
    width: 100%;
    max-height: 480px;
    height: auto;
    display: block;
    overflow: visible;
}

.axis-line {
    stroke: var(--color-text-primary);
    stroke-width: 1.5px;
}

.grid-line {
    stroke: var(--color-border-light);
    stroke-width: 1px;
    stroke-dasharray: 4,4;
}

.axis-tick {
    stroke: var(--color-text-muted);
    stroke-width: 1px;
}

.axis-label {
    fill: var(--color-text-secondary);
    font-size: 11px;
    font-family: var(--font-body);
}

.axis-title {
    fill: var(--color-text-primary);
    font-size: 12px;
    font-weight: 600;
    font-family: var(--font-heading);
}

.curve-path {
    fill: none;
    stroke-width: 3px;
    stroke-linecap: round;
    transition: stroke-dasharray 0.5s ease;
}

.offset-line {
    fill: none;
    stroke: #f59e0b;
    stroke-width: 1.5px;
    stroke-dasharray: 5,5;
}

.guide-line {
    fill: none;
    stroke: var(--color-text-muted);
    stroke-width: 1px;
    stroke-dasharray: 3,3;
}

.key-point {
    transition: r 0.2s ease, stroke-width 0.2s ease;
    cursor: pointer;
}

.key-point:hover {
    r: 7px;
    stroke-width: 3px;
}

/* Tooltip on Chart Overlay */
.chart-tooltip {
    position: absolute;
    background: rgba(26, 26, 26, 0.95);
    border: 1px solid rgba(255, 255, 255, 0.15);
    color: #ffffff;
    padding: 0.6rem 0.8rem;
    border-radius: 8px;
    font-size: 0.78rem;
    font-family: var(--font-body);
    pointer-events: none;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.25);
    z-index: 10;
    display: none;
    backdrop-filter: blur(8px);
}

body.dark-mode .chart-tooltip {
    background: rgba(245, 245, 245, 0.95);
    border: 1px solid rgba(0, 0, 0, 0.15);
    color: #1a1a1a;
}

.chart-tooltip div {
    margin-bottom: 0.2rem;
}

.chart-tooltip div:last-child {
    margin-bottom: 0;
}

.chart-tooltip strong {
    font-family: var(--font-mono);
}

/* Legend Styling */
.chart-legend {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    margin-top: 0.75rem;
    padding-top: 0.75rem;
    border-top: 1px solid var(--color-border-light);
    font-size: 0.8rem;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    font-weight: 500;
    color: var(--color-text-secondary);
}

.legend-color {
    width: 14px;
    height: 4px;
    border-radius: 2px;
}

/* Accordion Grid columns layout */
.accordion-grid {
    display: grid;
    grid-template-columns: minmax(0, 1fr) minmax(0, 1.2fr);
    gap: 1.2rem;
    align-items: start;
    width: 100%;
}

.accordion-col-left, .accordion-col-right {
    display: flex;
    flex-direction: column;
    gap: 1.2rem;
    width: 100%;
}

.table-container {
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: 10px;
    padding: 1rem;
    box-shadow: var(--shadow-sm);
}

.table-header {
    font-family: var(--font-heading);
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--color-text-primary);
    margin-bottom: 0.6rem;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.material-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.72rem;
    text-align: left;
}

.material-table th {
    font-weight: 600;
    color: var(--color-text-secondary);
    padding: 0.35rem 0.4rem;
    border-bottom: 1.5px solid var(--color-border);
    background: var(--color-bg-tertiary);
    line-height: 1.2;
}

.material-table th .unit {
    display: inline-block;
    font-size: 0.62rem;
    font-weight: 500;
    color: var(--color-text-muted);
    margin-top: 0.15rem;
}

.material-table td {
    padding: 0.35rem 0.4rem;
    border-bottom: 1px solid var(--color-border-light);
    color: var(--color-text-primary);
}

.material-table tr:hover td {
    background: rgba(220, 38, 38, 0.02);
}

/* Card layout for math info */
.info-card {
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: 10px;
    padding: 1rem;
    box-shadow: var(--shadow-sm);
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}

.info-card-title {
    font-family: var(--font-heading);
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--color-text-primary);
}

.info-card-text {
    font-size: 0.74rem;
    color: var(--color-text-secondary);
    line-height: 1.35;
}

.info-formula {
    background: var(--color-bg-tertiary);
    padding: 0.4rem;
    border-radius: 5px;
    text-align: center;
    border-left: 3px solid var(--color-accent);
    overflow-x: auto;
    color: var(--color-accent);
}

.info-formula .katex-display {
    margin: 0.2rem 0;
}

/* Download/Export Section */
.export-section {
    display: flex;
    gap: 0.75rem;
    justify-content: flex-end;
}

.export-btn {
    padding: 0.5rem 1rem;
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: 8px;
    color: var(--color-text-secondary);
    font-size: 0.8rem;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.4rem;
    transition: all 0.2s ease;
}

.export-btn:hover {
    color: var(--color-accent);
    border-color: var(--color-accent);
    background: var(--color-bg-tertiary);
}

/* Dark Mode overrides for direct elements */
body.dark-mode {
    --color-bg-primary: #0a0a0a;
    --color-bg-secondary: #1a1a1a;
    --color-bg-tertiary: #262626;
    --color-text-primary: #f3f4f6;
    --color-text-secondary: #d1d5db;
    --color-text-muted: #9ca3af;
    --color-border: #374151;
    --color-border-light: #1f2937;
    --color-elastic-bg: rgba(59, 130, 246, 0.08);
    --color-plastic-bg: rgba(239, 68, 68, 0.05);
}

body.dark-mode .curve-app-header {
    background: rgba(26, 26, 26, 0.85);
}

body.dark-mode .preset-btn.active {
    background: rgba(239, 68, 68, 0.08);
}

body.dark-mode .comp-item {
    background: var(--color-bg-tertiary);
}

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

/* Responsive adjustments */
@media (max-width: 1024px) {
    .curve-container {
        padding: 1rem;
    }
    .accordion-grid {
        grid-template-columns: 1fr;
    }
}