/* ==========================================================================
   1. Reset
   ========================================================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html, body {
    height: 100%;
}

body {
    font-family: 'Pretendard', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background-color: var(--color-bg);
    color: var(--color-text-primary);
    line-height: 1.6;
    transition: background-color 300ms ease, color 300ms ease;
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

button, input {
    font: inherit;
}

/* Screen reader only utility class */
.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;
}

/* ==========================================================================
   2. CSS Variables
   ========================================================================== */
:root {
    /* Brand & Utility Colors */
    --color-primary: #4F46E5;
    --color-primary-hover: #4338CA;
    --color-bg: #F8FAFC;
    --color-surface: #FFFFFF;
    --color-text-primary: #111827;
    --color-text-secondary: #6B7280;
    --color-border: #E5E7EB;
    --color-success: #22C55E;
    --color-warning: #F59E0B;
    --color-error: #EF4444;

    /* Spacing & Radii */
    --radius-btn: 12px;
    --radius-input: 12px;
    --radius-card: 16px;
    --radius-toast: 12px;

    /* Shadow */
    --shadow-main: 0 8px 24px rgba(0, 0, 0, 0.08);

    /* Layout */
    --max-width: 1200px;
}

/* Dark Mode Variable Overrides */
body.dark-mode {
    --color-bg: #111827;
    --color-surface: #1F2937;
    --color-text-primary: #F9FAFB;
    --color-text-secondary: #9CA3AF;
    --color-border: #374151;
    --shadow-main: 0 8px 24px rgba(0, 0, 0, 0.3);
}

/* ==========================================================================
   3. Typography
   ========================================================================== */
h1, h2, h3 {
    line-height: 1.2;
    font-weight: 700;
}

h1 {
    font-size: 2.5rem; /* 40px */
}

h2 {
    font-size: 2rem; /* 32px */
}

h3 {
    font-size: 1.5rem; /* 24px */
}

p {
    font-size: 1rem; /* 16px */
    color: var(--color-text-secondary);
}

/* ==========================================================================
   4. Layout
   ========================================================================== */
.header {
    background-color: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    position: sticky;
    top: 0;
    z-index: 100;
    transition: background-color 300ms ease, border-color 300ms ease;
}

.header-container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 1rem 48px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.75rem;
    color: var(--color-primary);
    letter-spacing: -0.02em;
}

.main-content {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 48px;
    min-height: calc(100vh - 160px);
}

.section {
    margin-bottom: 48px;
}

.section-title {
    margin-bottom: 24px;
}

.footer {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 24px 48px;
    text-align: center;
    border-top: 1px solid var(--color-border);
    color: var(--color-text-secondary);
    font-size: 0.875rem;
}

/* ==========================================================================
   5. Components
   ========================================================================== */
/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    height: 48px;
    padding: 0 24px;
    border-radius: var(--radius-btn);
    border: 1px solid transparent;
    cursor: pointer;
    font-weight: 600;
    transition: opacity 200ms ease, transform 150ms ease, background-color 200ms ease;
}

.btn:hover {
    opacity: 0.9;
}

.btn:active {
    transform: scale(0.98);
}

.btn:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

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

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

/* Upload Drop Zone */
.drop-zone {
    background-color: var(--color-surface);
    border: 2px dashed var(--color-border);
    border-radius: var(--radius-card);
    padding: 64px 32px;
    text-align: center;
    transition: border-color 300ms ease, background-color 300ms ease;
    cursor: pointer;
}

.drop-zone.drag-over, .drop-zone:hover {
    border-color: var(--color-primary);
    background-color: rgba(79, 70, 229, 0.04);
}

.drop-zone-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 16px;
}

.upload-icon {
    color: var(--color-primary);
}

.drop-zone-text {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--color-text-primary);
}

.drop-zone-subtext {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

.file-input {
    display: none;
}

.file-label {
    cursor: pointer;
}

/* Cards */
.card {
    background-color: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-card);
    padding: 24px;
    box-shadow: var(--shadow-main);
    transition: background-color 300ms ease, border-color 300ms ease;
}

.card-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 16px;
}

.card-title {
    font-size: 1.25rem;
    color: var(--color-text-primary);
}

/* Preview Layout */
.preview-layout {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
    margin-bottom: 24px;
}

.image-wrapper {
    width: 100%;
    max-height: 320px;
    overflow: hidden;
    border-radius: var(--radius-btn);
    background-color: var(--color-bg);
    display: flex;
    align-items: center;
    justify-content: center;
}

.preview-img {
    max-height: 320px;
    object-fit: contain;
}

.file-info {
    display: flex;
    justify-content: space-between;
    margin-top: 12px;
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

/* Statistics Grid */
.stats-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin-top: 16px;
}

.stat-item {
    display: flex;
    flex-direction: column;
    gap: 8px;
    padding: 16px;
    background-color: var(--color-bg);
    border-radius: var(--radius-btn);
}

.stat-label {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

.stat-value {
    font-size: 1.125rem;
    font-weight: 700;
    color: var(--color-text-primary);
}

.stat-color-box {
    display: flex;
    align-items: center;
    gap: 8px;
}

.color-dot {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    border: 1px solid rgba(0, 0, 0, 0.1);
}

/* Distribution Bar */
.distribution-card {
    margin-bottom: 24px;
}

.distribution-bar {
    display: flex;
    height: 16px;
    border-radius: 999px;
    overflow: hidden;
    margin-top: 16px;
    margin-bottom: 16px;
    background-color: var(--color-bg);
}

.distribution-segment {
    height: 100%;
    transition: width 300ms ease;
}

.distribution-legend {
    display: flex;
    flex-wrap: wrap;
    gap: 16px;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.875rem;
}

.legend-color-dot {
    width: 12px;
    height: 12px;
    border-radius: 50%;
}

.legend-hex {
    font-weight: 600;
}

.legend-percentage {
    color: var(--color-text-secondary);
}

/* Palette Grid */
.palette-section-card {
    margin-bottom: 24px;
}

.palette-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
    margin-top: 16px;
}

.palette-card {
    display: flex;
    flex-direction: column;
    gap: 12px;
    padding: 16px;
    border-radius: var(--radius-btn);
    background-color: var(--color-bg);
    border: 1px solid var(--color-border);
}

.color-preview {
    height: 100px;
    border-radius: var(--radius-btn);
    box-shadow: inset 0 0 0 1px rgba(0, 0, 0, 0.05);
}

.color-details {
    display: flex;
    flex-direction: column;
}

.color-hex {
    font-weight: 700;
    font-size: 1.125rem;
    color: var(--color-text-primary);
}

.color-rgb {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

/* Toast Container */
.toast-container {
    position: fixed;
    bottom: 24px;
    right: 24px;
    display: flex;
    flex-direction: column;
    gap: 12px;
    z-index: 1000;
}

.toast {
    padding: 16px 24px;
    border-radius: var(--radius-toast);
    background-color: var(--color-surface);
    color: var(--color-text-primary);
    box-shadow: var(--shadow-main);
    border-left: 4px solid var(--color-primary);
    font-weight: 600;
    opacity: 1;
    transition: opacity 300ms ease, transform 300ms ease;
}

.toast-success {
    border-left-color: var(--color-success);
}

.toast-error {
    border-left-color: var(--color-error);
}

.toast-warning {
    border-left-color: var(--color-warning);
}

.toast.fade-out {
    opacity: 0;
    transform: translateY(10px);
}

/* ==========================================================================
   6. Utilities
   ========================================================================== */
.hidden {
    display: none !important;
}

/* ==========================================================================
   7. Responsive
   ========================================================================== */
@media (max-width: 1024px) {
    .header-container, .main-content, .footer {
        padding-left: 32px;
        padding-right: 32px;
    }

    .palette-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 767px) {
    .header-container, .main-content, .footer {
        padding-left: 20px;
        padding-right: 20px;
    }

    .preview-layout {
        grid-template-columns: 1fr;
    }

    .stats-grid {
        grid-template-columns: 1fr;
    }

    .palette-grid {
        grid-template-columns: 1fr;
    }

    .btn {
        width: 100%;
    }
}