/* ========================================
   RESET & BASE STYLES
   ======================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --color-bg: #ffffff;
    --color-text: #000000;
    --color-border: #000000;
    --color-hover: #f5f5f5;
    --color-active: #e8e8e8;
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --border-width: 2px;
    --border-radius: 0;
    --transition: all 0.2s ease;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', sans-serif;
    background-color: var(--color-bg);
    color: var(--color-text);
    line-height: 1.6;
    min-height: 100vh;
}

/* ========================================
   LAYOUT
   ======================================== */
.container {
    max-width: 100%;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.header {
    padding: var(--spacing-md) var(--spacing-lg);
    border-bottom: var(--border-width) solid var(--color-border);
    background-color: var(--color-bg);
}

.header h1 {
    font-size: 1.5rem;
    font-weight: 600;
    letter-spacing: -0.02em;
}

/* Main Content Area */
.main-content {
    display: grid;
    grid-template-columns: 1fr;
    grid-template-rows: auto 1fr;
    flex: 1;
    overflow: hidden;
}

/* Desktop: Two columns */
@media (min-width: 768px) {
    .main-content {
        grid-template-columns: 400px 1fr;
        grid-template-rows: 1fr;
    }
}

@media (min-width: 1024px) {
    .main-content {
        grid-template-columns: 480px 1fr;
        grid-template-rows: 1fr;
    }
}

/* ========================================
   INPUT PANEL (LEFT COLUMN)
   ======================================== */
.input-panel {
    padding: var(--spacing-lg);
    border-right: var(--border-width) solid var(--color-border);
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
    background-color: var(--color-bg);
    overflow-y: auto;
}

/* Mobile Toggle Button */
.mobile-toggle {
    display: none;
    width: 100%;
    padding: var(--spacing-sm);
    border: none;
    border-bottom: var(--border-width) solid var(--color-border);
    background-color: var(--color-bg);
    color: var(--color-text);
    font-size: 0.875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    cursor: pointer;
    transition: var(--transition);
    text-align: left;
    align-items: center;
    gap: var(--spacing-xs);
}

.mobile-toggle:hover {
    background-color: var(--color-hover);
}

.toggle-icon {
    font-size: 0.75rem;
    transition: transform 0.3s ease;
}

.input-panel.collapsed .toggle-icon {
    transform: rotate(-90deg);
}

.panel-content {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

@media (max-width: 767px) {
    .mobile-toggle {
        display: flex;
    }

    .input-panel {
        border-right: none;
        border-bottom: var(--border-width) solid var(--color-border);
        max-height: none;
        min-height: auto;
        overflow: visible;
        padding: 0;
    }

    .panel-content {
        max-height: 25vh;
        overflow-y: auto;
        padding: var(--spacing-xs) var(--spacing-sm);
        gap: var(--spacing-xs);
        transition: max-height 0.3s ease, padding 0.3s ease;
    }

    .input-panel.collapsed .panel-content {
        max-height: 0;
        padding: 0 var(--spacing-sm);
        overflow: hidden;
    }
}

.section-title {
    font-size: 0.875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--spacing-sm);
}

/* File Upload Area */
.upload-area {
    border: var(--border-width) dashed var(--color-border);
    padding: var(--spacing-xl);
    text-align: center;
    cursor: pointer;
    transition: var(--transition);
    background-color: var(--color-bg);
}

.upload-area:hover {
    background-color: var(--color-hover);
}

.upload-area.drag-over {
    background-color: var(--color-active);
    border-style: solid;
}

.upload-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-sm);
    display: block;
}

.upload-text {
    font-size: 0.875rem;
    margin-bottom: var(--spacing-xs);
}

.upload-hint {
    font-size: 0.75rem;
    color: #666;
}

/* File Input (Hidden) */
.file-input {
    display: none;
}

/* File Info */
.file-info {
    padding: var(--spacing-md);
    border: var(--border-width) solid var(--color-border);
    background-color: var(--color-bg);
    display: none;
}

.file-info.active {
    display: block;
}

.file-name {
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
    word-break: break-all;
}

.file-size {
    font-size: 0.875rem;
    color: #666;
}

/* Buttons */
.button-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.btn {
    padding: var(--spacing-sm) var(--spacing-md);
    border: var(--border-width) solid var(--color-border);
    background-color: var(--color-bg);
    color: var(--color-text);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    text-align: center;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.btn:hover:not(:disabled) {
    background-color: var(--color-text);
    color: var(--color-bg);
}

.btn:active:not(:disabled) {
    transform: translateY(1px);
}

.btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

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

.btn-primary:hover:not(:disabled) {
    background-color: var(--color-bg);
    color: var(--color-text);
}

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

/* Theme Selector */
.theme-select {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    border: var(--border-width) solid var(--color-border);
    background-color: var(--color-bg);
    color: var(--color-text);
    font-size: 0.875rem;
    font-weight: 400;
    cursor: pointer;
    transition: var(--transition);
    font-family: inherit;
}

.theme-select:hover {
    background-color: var(--color-hover);
}

.theme-select:focus {
    outline: none;
    background-color: var(--color-active);
}

/* ========================================
   PREVIEW PANEL (RIGHT COLUMN)
   ======================================== */
.preview-panel {
    display: flex;
    flex-direction: column;
    background-color: var(--color-bg);
    overflow: hidden;
}

.preview-header {
    padding: var(--spacing-md) var(--spacing-lg);
    border-bottom: var(--border-width) solid var(--color-border);
    display: flex;
    justify-content: space-between;
    align-items: center;
    background-color: var(--color-bg);
}

.preview-title {
    font-size: 0.875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.download-btn {
    padding: var(--spacing-xs) var(--spacing-md);
    border: var(--border-width) solid var(--color-border);
    background-color: var(--color-bg);
    color: var(--color-text);
    font-size: 0.75rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.download-btn:hover:not(:disabled) {
    background-color: var(--color-text);
    color: var(--color-bg);
}

.download-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

.preview-content {
    flex: 1;
    overflow: auto;
    position: relative;
}

/* Empty State */
.empty-state {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 100%;
    padding: var(--spacing-xl);
    text-align: center;
    color: #999;
}

.empty-icon {
    font-size: 4rem;
    margin-bottom: var(--spacing-md);
}

.empty-text {
    font-size: 1rem;
    margin-bottom: var(--spacing-xs);
}

.empty-hint {
    font-size: 0.875rem;
}

/* Notebook Frame */
.notebook-frame {
    width: 100%;
    height: 100%;
    border: none;
    display: none;
}

.notebook-frame.active {
    display: block;
}

/* ========================================
   LOADING STATE
   ======================================== */
.loading {
    display: none;
    padding: var(--spacing-lg);
    text-align: center;
}

.loading.active {
    display: block;
}

.loading-spinner {
    width: 40px;
    height: 40px;
    border: 3px solid var(--color-border);
    border-top-color: transparent;
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
    margin: 0 auto var(--spacing-md);
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

.loading-text {
    font-size: 0.875rem;
    color: #666;
}

/* ========================================
   RESPONSIVE ADJUSTMENTS
   ======================================== */
@media (max-width: 767px) {
    .header {
        padding: var(--spacing-xs) var(--spacing-md);
    }

    .header h1 {
        font-size: 1rem;
    }

    .input-panel {
        padding: var(--spacing-xs) var(--spacing-sm);
        gap: var(--spacing-xs);
    }

    .section-title {
        font-size: 0.6875rem;
        margin-bottom: 0.25rem;
    }

    .upload-area {
        padding: var(--spacing-sm);
    }

    .upload-icon {
        font-size: 1.5rem;
        margin-bottom: 0.25rem;
    }

    .upload-text {
        font-size: 0.75rem;
        margin-bottom: 0.125rem;
    }

    .upload-hint {
        font-size: 0.625rem;
    }

    .file-info {
        padding: var(--spacing-xs);
    }

    .file-name {
        font-size: 0.75rem;
        margin-bottom: 0.125rem;
    }

    .file-size {
        font-size: 0.6875rem;
    }

    .preview-header {
        padding: var(--spacing-xs) var(--spacing-sm);
    }

    .preview-title {
        font-size: 0.6875rem;
    }

    .download-btn {
        font-size: 0.625rem;
        padding: 0.25rem var(--spacing-xs);
    }

    .button-group {
        gap: 0.25rem;
    }

    .btn {
        padding: 0.375rem var(--spacing-xs);
        font-size: 0.6875rem;
    }

    .empty-state {
        padding: var(--spacing-xs);
    }

    .empty-icon {
        font-size: 2.5rem;
        margin-bottom: var(--spacing-xs);
    }

    .empty-text {
        font-size: 0.8125rem;
        margin-bottom: 0.125rem;
    }

    .empty-hint {
        font-size: 0.6875rem;
    }
}

/* ========================================
   UTILITY CLASSES
   ======================================== */
.hidden {
    display: none !important;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
}