/* ==========================================================================
   Design Tokens & CSS Variables (Design System Core)
   ========================================================================== */
:root {
    /* Color Palette - Surfaces & Backgrounds */
    --color-bg-base: #0f172a;
    --color-bg-surface: #1e293b;
    --color-bg-subtle: rgba(15, 23, 42, 0.55);
    
    /* Color Palette - Text & Typography */
    --color-text-primary: #f8fafc;
    --color-text-secondary: #cbd5e1;
    --color-text-muted: #94a3b8;
    
    /* Color Palette - Accents & States */
    --color-accent: #10b981;
    --color-accent-hover: #059669;
    --color-accent-focus: #34d399;
    --color-accent-subtle: rgba(16, 185, 129, 0.12);
    --color-accent-border: rgba(16, 185, 129, 0.25);
    
    --color-danger: #f43f5e;
    --color-danger-hover: #e11d48;
    --color-danger-subtle: rgba(244, 63, 94, 0.15);
    
    --color-border: #334155;
    --color-border-subtle: rgba(51, 65, 85, 0.6);

    /* Social Progress Colors */
    --color-bar-sky: #38bdf8;
    --color-bar-emerald: #10b981;
    --color-bar-blue: #3b82f6;
    --color-bar-indigo: #6366f1;

    /* Typography Scale */
    --font-family-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans TC", sans-serif;
    --font-size-xs: 0.75rem;     /* 12px */
    --font-size-sm: 0.875rem;    /* 14px */
    --font-size-base: 1rem;      /* 16px */
    --font-size-lg: 1.25rem;     /* 20px */
    --font-size-xl: 1.5rem;      /* 24px */
    --line-height-normal: 1.5;
    --line-height-relaxed: 1.625;

    /* Spacing System */
    --space-1: 0.25rem;
    --space-2: 0.5rem;
    --space-3: 0.75rem;
    --space-4: 1rem;
    --space-6: 1.5rem;
    --space-8: 2rem;

    /* Radii */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-full: 9999px;

    /* Transitions & Animations */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-normal: 200ms cubic-bezier(0.4, 0, 0.2, 1);
    --shadow-focus: 0 0 0 2px var(--color-bg-base), 0 0 0 4px var(--color-accent);
}

/* ==========================================================================
   CSS Reset & Base Rules
   ========================================================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    background-color: var(--color-bg-base);
    color: var(--color-text-primary);
    font-family: var(--font-family-sans);
    line-height: var(--line-height-normal);
    min-height: 100vh;
    padding: var(--space-4);
    text-rendering: optimizeLegibility;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

::selection {
    background-color: var(--color-accent);
    color: var(--color-bg-base);
}

/* ==========================================================================
   Accessibility & Focus System (WCAG 2.1 AA Compliant)
   ========================================================================== */
*:focus {
    outline: none;
}

*:focus-visible {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
}

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

/* ==========================================================================
   Layout Containers
   ========================================================================== */
.container {
    max-width: 56rem;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: var(--space-6);
}

.header {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--color-border);
    padding-bottom: var(--space-4);
    gap: var(--space-4);
}

#app-title {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--color-accent-focus);
    letter-spacing: -0.02em;
}

#app-subtitle {
    font-size: var(--font-size-xs);
    color: var(--color-text-muted);
    margin-top: var(--space-1);
}

.header-actions {
    display: flex;
    align-items: center;
    gap: var(--space-3);
}

.badge {
    background-color: var(--color-accent-subtle);
    color: var(--color-accent-focus);
    border: 1px solid var(--color-accent-border);
    font-size: var(--font-size-xs);
    padding: var(--space-1) var(--space-3);
    border-radius: var(--radius-full);
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.badge-dot {
    width: 0.5rem;
    height: 0.5rem;
    border-radius: var(--radius-full);
    background-color: var(--color-accent-focus);
    animation: pulse 2s cubic-bezier(0.4, 0, 0.6, 1) infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; transform: scale(1); }
    50% { opacity: 0.4; transform: scale(0.85); }
}

/* Language Switcher */
#btn-lang {
    background-color: var(--color-bg-surface);
    color: var(--color-text-secondary);
    border: 1px solid var(--color-border);
    font-size: var(--font-size-xs);
    padding: var(--space-1) var(--space-3);
    border-radius: var(--radius-md);
    cursor: pointer;
    font-weight: 500;
    transition: background-color var(--transition-fast), border-color var(--transition-fast);
}

#btn-lang:hover {
    background-color: #273549;
    border-color: var(--color-text-muted);
}

#btn-lang:active {
    transform: scale(0.97);
}

/* ==========================================================================
   Main Grid & Editor Area
   ========================================================================== */
.main-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--space-6);
}

.editor-col {
    display: flex;
    flex-direction: column;
    gap: var(--space-4);
}

textarea {
    width: 100%;
    height: 18rem;
    padding: var(--space-4);
    background-color: var(--color-bg-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    color: var(--color-text-primary);
    font-family: inherit;
    font-size: var(--font-size-sm);
    line-height: var(--line-height-relaxed);
    resize: none;
    transition: border-color var(--transition-normal), box-shadow var(--transition-normal);
}

textarea:focus {
    border-color: var(--color-accent);
    box-shadow: 0 0 0 3px var(--color-accent-subtle);
}

textarea::placeholder {
    color: var(--color-text-muted);
    opacity: 0.8;
}

/* ==========================================================================
   Button System (Interactive States & Resilience)
   ========================================================================== */
.button-group {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: var(--space-2);
}

.btn {
    font-size: var(--font-size-xs);
    font-weight: 500;
    padding: 0.45rem var(--space-3);
    border-radius: var(--radius-md);
    cursor: pointer;
    border: 1px solid transparent;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    user-select: none;
    transition: background-color var(--transition-fast), 
                transform var(--transition-fast), 
                box-shadow var(--transition-fast), 
                opacity var(--transition-fast);
}

.btn:active {
    transform: scale(0.97);
}

.btn:disabled {
    opacity: 0.45;
    cursor: not-allowed;
    pointer-events: none;
}

.btn-primary {
    background-color: var(--color-accent);
    color: #ffffff;
}

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

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

.btn-secondary:hover {
    background-color: #475569;
}

.btn-danger {
    background-color: var(--color-danger-subtle);
    color: #fca5a5;
    border-color: rgba(244, 63, 94, 0.2);
    margin-left: auto;
}

.btn-danger:hover {
    background-color: rgba(244, 63, 94, 0.25);
    color: #ffffff;
}

/* ==========================================================================
   Cards & Statistics Panel
   ========================================================================== */
.stats-col {
    display: flex;
    flex-direction: column;
    gap: var(--space-4);
}

.card {
    background-color: var(--color-bg-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--space-4);
    display: flex;
    flex-direction: column;
    gap: var(--space-3);
}

.card h2 {
    font-size: var(--font-size-xs);
    font-weight: 600;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.stats-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--space-3);
}

.stat-box {
    background-color: var(--color-bg-subtle);
    padding: var(--space-3);
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border-subtle);
}

.stat-label {
    font-size: var(--font-size-xs);
    color: var(--color-text-muted);
}

.stat-value {
    font-size: var(--font-size-lg);
    font-weight: 700;
    color: var(--color-text-primary);
    margin-top: var(--space-1);
    font-variant-numeric: tabular-nums;
}

.text-emerald {
    color: var(--color-accent-focus);
    font-size: var(--font-size-xl);
}

.read-time-row {
    font-size: var(--font-size-xs);
    color: var(--color-text-muted);
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: var(--space-2);
    border-top: 1px solid var(--color-border-subtle);
}

#stat-read-time {
    color: var(--color-text-secondary);
    font-weight: 500;
}

/* ==========================================================================
   Social Media Character Counters & Progress Bars
   ========================================================================== */
.limit-item {
    display: flex;
    flex-direction: column;
    gap: var(--space-1);
}

.limit-label-row {
    display: flex;
    justify-content: space-between;
    font-size: var(--font-size-xs);
    color: var(--color-text-secondary);
    font-variant-numeric: tabular-nums;
}

.limit-exceeded {
    color: var(--color-danger) !important;
    font-weight: 700;
}

.progress-track {
    width: 100%;
    background-color: var(--color-bg-base);
    height: 0.375rem;
    border-radius: var(--radius-full);
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    width: 0%;
    transition: width var(--transition-normal), background-color var(--transition-fast);
}

.bar-sky { background-color: var(--color-bar-sky); }
.bar-emerald { background-color: var(--color-bar-emerald); }
.bar-blue { background-color: var(--color-bar-blue); }
.bar-indigo { background-color: var(--color-bar-indigo); }
.bar-exceeded { background-color: var(--color-danger) !important; }

/* ==========================================================================
   Responsive Breakpoints
   ========================================================================== */
/* Extra Small Screens (< 420px) */
@media (max-width: 420px) {
    body {
        padding: var(--space-2);
    }
    
    .container {
        gap: var(--space-4);
    }
    
    #app-title {
        font-size: var(--font-size-lg);
    }
    
    textarea {
        height: 13rem;
        padding: var(--space-3);
    }

    .button-group {
        gap: 0.375rem;
    }

    .btn {
        font-size: 0.7rem;
        padding: 0.35rem 0.5rem;
    }

    .btn-danger {
        margin-left: 0;
        width: 100%;
    }
}

/* Tablet & Desktop Screens (>= 768px) */
@media (min-width: 768px) {
    body {
        padding: var(--space-8);
    }

    .main-grid {
        grid-template-columns: 2fr 1fr;
    }
}

/* Large Screens (>= 1280px) */
@media (min-width: 1280px) {
    .container {
        max-width: 64rem;
    }

    textarea {
        height: 22rem;
    }
}

/* ==========================================================================
   Print Stylesheet (Privacy & Clean Export Compliant)
   ========================================================================== */
@media print {
    body {
        background-color: #ffffff !important;
        color: #000000 !important;
        padding: 0;
    }

    .header-actions,
    .button-group,
    #btn-lang,
    .badge {
        display: none !important;
    }

    .card, textarea, .stat-box {
        background: transparent !important;
        border: 1px solid #cccccc !important;
        color: #000000 !important;
    }

    .progress-track {
        border: 1px solid #999999;
    }
}