:root {
    /* Light Mode */
    --bg-color: #F5F5F7;
    --bg-secondary: #FFFFFF;
    --card-bg: rgba(255, 255, 255, 0.8);
    --text-primary: #1D1D1F;
    --text-secondary: #86868B;
    --accent: #007AFF;
    --accent-hover: #0062cc;
    --border: rgba(0, 0, 0, 0.1);
    --input-bg: rgba(0, 0, 0, 0.05);
    --danger: #FF3B30;
    --success: #34C759;
    --font-family: -apple-system, BlinkMacSystemFont, "Inter", "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    --shadow-sm: 0 4px 12px rgba(0, 0, 0, 0.05);
    --shadow-lg: 0 20px 40px rgba(0, 0, 0, 0.1);
    --brand-gradient: linear-gradient(135deg, #007AFF 0%, #5856D6 100%);
    
    /* Animation Variables */
    --ease-spring: cubic-bezier(0.16, 1, 0.3, 1);
    --duration-normal: 0.3s;
    --duration-fast: 0.2s;
}

@media (prefers-color-scheme: dark) {
    :root {
        --bg-color: #000000;
        --bg-secondary: #1C1C1E;
        --card-bg: rgba(28, 28, 30, 0.8);
        --text-primary: #F5F5F7;
        --text-secondary: #98989D;
        --border: rgba(255, 255, 255, 0.1);
        --input-bg: rgba(255, 255, 255, 0.1);
        --shadow-sm: 0 4px 12px rgba(0, 0, 0, 0.3);
        --shadow-lg: 0 20px 40px rgba(0, 0, 0, 0.5);
    }
}

/* Manual Dark Mode */
body.dark-mode {
    --bg-color: #000000;
    --bg-secondary: #1C1C1E;
    --card-bg: rgba(28, 28, 30, 0.8);
    --text-primary: #F5F5F7;
    --text-secondary: #98989D;
    --border: rgba(255, 255, 255, 0.1);
    --input-bg: rgba(255, 255, 255, 0.1);
    --shadow-sm: 0 4px 12px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 20px 40px rgba(0, 0, 0, 0.5);
}

/* Manual Light Mode */
body.light-mode {
    --bg-color: #F5F5F7;
    --bg-secondary: #FFFFFF;
    --card-bg: rgba(255, 255, 255, 0.8);
    --text-primary: #1D1D1F;
    --text-secondary: #86868B;
    --accent: #007AFF;
    --accent-hover: #0062cc;
    --border: rgba(0, 0, 0, 0.1);
    --input-bg: rgba(0, 0, 0, 0.05);
    --danger: #FF3B30;
    --success: #34C759;
    --shadow-sm: 0 4px 12px rgba(0, 0, 0, 0.05);
    --shadow-lg: 0 20px 40px rgba(0, 0, 0, 0.1);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--text-primary);
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    transition: background-color var(--duration-normal) ease, color var(--duration-normal) ease;
}

/* --- Layout Structure --- */

.layout-wrapper {
    display: grid;
    grid-template-columns: 1fr 1fr;
    min-height: 100vh;
    width: 100%;
}

/* Brand Section (Desktop) */
.brand-section {
    background: var(--bg-color);
    display: flex;
    flex-direction: column;
    justify-content: center;
    padding: 80px;
    position: relative;
    overflow: hidden;
    border-right: 1px solid var(--border);
}

.brand-content {
    position: relative;
    z-index: 2;
    max-width: 480px;
    margin: 0 auto;
}

.brand-logo-large {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-bottom: 24px;
}

.brand-logo-large h1 {
    font-size: 32px;
    font-weight: 700;
    letter-spacing: -0.03em;
}

.icon-large {
    width: 48px;
    height: 48px;
    background: var(--brand-gradient);
    border-radius: 12px;
    box-shadow: 0 8px 24px rgba(0, 122, 255, 0.3);
}

.brand-tagline {
    font-size: 24px;
    line-height: 1.4;
    color: var(--text-secondary);
    margin-bottom: 48px;
    font-weight: 500;
}

.brand-features {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.feature-item {
    display: flex;
    align-items: center;
    gap: 16px;
    font-size: 16px;
    font-weight: 500;
    color: var(--text-primary);
}

.feature-icon {
    width: 40px;
    height: 40px;
    background: var(--input-bg);
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--accent);
}

.brand-bg-effect {
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: radial-gradient(circle at 50% 50%, rgba(0, 122, 255, 0.08), transparent 60%);
    z-index: 1;
    pointer-events: none;
}

/* App Section */
.app-section {
    background: var(--bg-secondary);
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 40px;
    position: relative;
}

.app-container {
    width: 100%;
    max-width: 420px;
    display: flex;
    flex-direction: column;
    gap: 24px;
    animation: fadeIn var(--duration-normal) ease-out backwards;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: scale(0.98);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

/* Header */
header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 4px;
    height: 48px;
}

.logo {
    display: flex;
    align-items: center;
    gap: 12px;
}

.logo .icon {
    width: 32px;
    height: 32px;
    background: var(--brand-gradient);
    border-radius: 8px;
    box-shadow: 0 4px 12px rgba(0, 122, 255, 0.3);
}

.logo h1 {
    font-size: 20px;
    font-weight: 700;
    letter-spacing: -0.02em;
}

.header-right {
    display: flex;
    align-items: center;
    gap: 12px;
}

.icon-btn {
    background: var(--input-bg);
    border: 1px solid transparent;
    color: var(--text-primary);
    width: 36px;
    height: 36px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--duration-fast) var(--ease-spring);
}

.icon-btn:hover {
    transform: scale(1.05);
    background: var(--border);
}

.status-indicator {
    font-size: 13px;
    font-weight: 500;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: 8px;
    background: var(--input-bg);
    padding: 6px 12px;
    border-radius: 20px;
    border: 1px solid transparent;
    transition: all var(--duration-normal) var(--ease-spring);
}

.status-indicator::before {
    content: '';
    display: block;
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background-color: var(--text-secondary);
    transition: background-color 0.3s;
}

.status-indicator.connected::before {
    background-color: var(--success);
    box-shadow: 0 0 8px rgba(52, 199, 89, 0.5);
}

/* Cards & Content */
.card {
    background: var(--card-bg);
    border-radius: 24px;
    padding: 32px;
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    transition: transform var(--duration-normal) var(--ease-spring), background-color var(--duration-normal) ease;
}

h2 {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 8px;
}

.description {
    color: var(--text-secondary);
    font-size: 15px;
    margin-bottom: 24px;
    line-height: 1.5;
}

.input-group {
    display: flex;
    gap: 12px;
}

input[type="text"],
textarea {
    width: 100%;
    padding: 14px 16px;
    border-radius: 12px;
    border: 1px solid transparent;
    background-color: var(--input-bg);
    color: var(--text-primary);
    font-family: inherit;
    font-size: 16px;
    outline: none;
    transition: all 0.2s;
}

input[type="text"]:focus,
textarea:focus {
    background-color: var(--card-bg);
    border-color: var(--accent);
    box-shadow: 0 0 0 4px rgba(0, 122, 255, 0.1);
    transform: scale(1.01);
}

button {
    cursor: pointer;
    border: none;
    font-family: inherit;
    font-weight: 600;
    border-radius: 12px;
    transition: all var(--duration-fast) var(--ease-spring);
}

button:active {
    transform: scale(0.95);
}

#pair-btn {
    background-color: var(--accent);
    color: white;
    padding: 0 24px;
    font-size: 15px;
}

#pair-btn:hover {
    background-color: var(--accent-hover);
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(0, 122, 255, 0.3);
}

.hidden {
    display: none !important;
}

/* Tabs */
.tabs {
    display: flex;
    background: var(--input-bg);
    padding: 4px;
    border-radius: 14px;
    margin-bottom: 24px;
    position: relative;
}

.tab-btn {
    flex: 1;
    padding: 10px;
    background: transparent;
    color: var(--text-secondary);
    font-size: 14px;
    border-radius: 10px;
    position: relative;
    z-index: 1;
    transition: all var(--duration-fast) ease;
}

.tab-btn:hover {
    color: var(--text-primary);
}

.tab-btn.active {
    color: var(--text-primary);
    background: var(--card-bg);
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    transform: scale(1);
}

/* Tab Content */
.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
    animation: tabEnter var(--duration-normal) var(--ease-spring) forwards;
}

@keyframes tabEnter {
    0% {
        opacity: 0;
        transform: scale(0.98);
    }
    100% {
        opacity: 1;
        transform: scale(1);
    }
}

textarea {
    min-height: 160px;
    resize: none;
    margin-bottom: 24px;
    line-height: 1.5;
}

.primary-btn {
    width: 100%;
    padding: 16px;
    background: var(--brand-gradient);
    color: white;
    font-size: 16px;
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 10px;
    box-shadow: 0 4px 12px rgba(0, 122, 255, 0.25);
}

.primary-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(0, 122, 255, 0.35);
}

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

.primary-btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

/* File Upload */
.file-drop-area {
    border: 2px dashed var(--border);
    border-radius: 16px;
    padding: 48px 24px;
    text-align: center;
    cursor: pointer;
    transition: all var(--duration-fast) var(--ease-spring);
    position: relative;
    margin-bottom: 24px;
    background: rgba(0,0,0,0.02);
}

.file-drop-area:hover {
    border-color: var(--accent);
    background: rgba(0, 122, 255, 0.05);
    transform: scale(1.01);
}

.file-drop-area p {
    color: var(--text-secondary);
    margin-top: 16px;
    font-size: 15px;
    font-weight: 500;
}

.upload-icon {
    color: var(--text-secondary);
    transition: all var(--duration-fast) var(--ease-spring);
}

.file-drop-area:hover .upload-icon {
    color: var(--accent);
    transform: translateY(-4px);
}

#file-input {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    opacity: 0;
    cursor: pointer;
}

#file-preview {
    background: var(--input-bg);
    border: 1px solid transparent;
    border-radius: 14px;
    padding: 16px;
    margin-bottom: 24px;
    animation: fadeIn var(--duration-normal) var(--ease-spring);
}

.file-info {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 14px;
    font-weight: 500;
}

#remove-file-btn {
    background: rgba(0,0,0,0.05);
    color: var(--text-secondary);
    width: 24px;
    height: 24px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 16px;
    padding: 0;
}

#remove-file-btn:hover {
    background: var(--danger);
    color: white;
    transform: rotate(90deg);
}

.progress-bar {
    height: 6px;
    background: rgba(0,0,0,0.05);
    border-radius: 3px;
    margin-top: 12px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: var(--accent);
    width: 0%;
    transition: width 0.3s ease-out;
    border-radius: 3px;
}

/* Toast */
.toast {
    position: fixed;
    bottom: 40px;
    left: 50%;
    transform: translateX(-50%);
    background: rgba(0,0,0,0.8);
    color: white;
    padding: 12px 24px;
    border-radius: 30px;
    font-size: 14px;
    font-weight: 500;
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    box-shadow: 0 10px 30px rgba(0,0,0,0.2);
    animation: toastSpring 0.5s var(--ease-spring) forwards;
    z-index: 100;
}

@keyframes toastSpring {
    0% {
        opacity: 0;
        transform: translate(-50%, 20px) scale(0.9);
    }
    100% {
        opacity: 1;
        transform: translate(-50%, 0) scale(1);
    }
}

/* --- Responsive Design --- */

.mobile-only {
    display: none !important;
}

@media (max-width: 768px) {
    .layout-wrapper {
        grid-template-columns: 1fr;
    }

    .brand-section {
        display: none;
    }

    .app-section {
        padding: 0;
        align-items: flex-start;
        background: var(--bg-color);
    }

    .app-container {
        max-width: 100%;
        min-height: 100vh;
        padding: 16px;
        gap: 20px;
    }

    .card {
        box-shadow: none;
        border: none;
        background: transparent;
        padding: 0;
        backdrop-filter: none;
    }

    .mobile-only {
        display: flex !important;
    }

    .desktop-only {
        display: none !important;
    }

    /* Adjust inputs for touch */
    input[type="text"],
    textarea,
    button {
        font-size: 16px; /* Prevent zoom on iOS */
    }

    .file-drop-area {
        padding: 32px 20px;
    }
}