:root {
    --color-primary: #0052CC;
    --color-primary-hover: #0065FF;
    --color-secondary: #42526E;
    --color-success: #00875A;
    --color-danger: #DE350B;
    --color-warning: #FF991F;
    --color-bg-primary: #FFFFFF;
    --color-bg-secondary: #F4F5F7;
    --color-bg-tertiary: #FAFBFC;
    --color-border: #DFE1E6;
    --color-text-primary: #172B4D;
    --color-text-secondary: #6B778C;
    --color-text-inverse: #FFFFFF;
    --shadow-sm: 0 1px 1px rgba(9,30,66,0.25), 0 0 1px rgba(9,30,66,0.13);
    --shadow-md: 0 8px 12px rgba(9,30,66,0.15), 0 0 1px rgba(9,30,66,0.13);
    --shadow-lg: 0 20px 32px rgba(9,30,66,0.15), 0 0 1px rgba(9,30,66,0.13);
    --radius-sm: 3px;
    --radius-md: 4px;
    --radius-lg: 8px;
    --transition-fast: 200ms;
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
}

body.dark-theme {
    --color-primary: #4C9AFF;
    --color-primary-hover: #2684FF;
    --color-secondary: #8993A4;
    --color-bg-primary: #1D2125;
    --color-bg-secondary: #22272B;
    --color-bg-tertiary: #282E33;
    --color-border: #38414A;
    --color-text-primary: #B6C2CF;
    --color-text-secondary: #8C9BAB;
    --shadow-sm: 0 1px 1px rgba(0,0,0,0.5), 0 0 1px rgba(0,0,0,0.25);
    --shadow-md: 0 8px 12px rgba(0,0,0,0.5), 0 0 1px rgba(0,0,0,0.25);
    --shadow-lg: 0 20px 32px rgba(0,0,0,0.5), 0 0 1px rgba(0,0,0,0.25);
}

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

body {
    font-family: var(--font-family);
    background-color: var(--color-bg-tertiary);
    color: var(--color-text-primary);
    line-height: 1.5;
    transition: background-color var(--transition-fast), color var(--transition-fast);
}

.app-container {
    height: 100vh;
    display: flex;
    flex-direction: column;
}

.app-header {
    background-color: var(--color-bg-primary);
    border-bottom: 1px solid var(--color-border);
    padding: 0 24px;
    box-shadow: var(--shadow-sm);
}

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 56px;
}

.app-title {
    display: flex;
    align-items: center;
    gap: 12px;
    font-size: 20px;
    font-weight: 600;
    color: var(--color-text-primary);
}

.logo {
    width: 32px;
    height: 32px;
    color: var(--color-primary);
}

.nav-actions {
    display: flex;
    align-items: center;
    gap: 16px;
}

.btn-icon {
    width: 32px;
    height: 32px;
    border: none;
    background: transparent;
    color: var(--color-text-secondary);
    cursor: pointer;
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition-fast);
}

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

.btn-icon svg {
    width: 20px;
    height: 20px;
}

.language-selector {
    padding: 4px 8px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    background-color: var(--color-bg-primary);
    color: var(--color-text-primary);
    font-size: 14px;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.language-selector:hover {
    border-color: var(--color-primary);
}

.main-content {
    flex: 1;
    display: flex;
    overflow: hidden;
}

.sidebar {
    width: 320px;
    background-color: var(--color-bg-primary);
    border-right: 1px solid var(--color-border);
    display: flex;
    flex-direction: column;
}

.sidebar-header {
    padding: 20px;
    border-bottom: 1px solid var(--color-border);
}

.sidebar-header h2 {
    font-size: 16px;
    font-weight: 600;
    margin-bottom: 16px;
    color: var(--color-text-primary);
}

.btn-primary {
    width: 100%;
    padding: 8px 16px;
    background-color: var(--color-primary);
    color: var(--color-text-inverse);
    border: none;
    border-radius: var(--radius-sm);
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    transition: all var(--transition-fast);
}

.btn-primary:hover {
    background-color: var(--color-primary-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-primary svg {
    width: 16px;
    height: 16px;
}

.search-box {
    padding: 12px 20px;
    position: relative;
}

.search-box input {
    width: 100%;
    padding: 8px 12px 8px 36px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    background-color: var(--color-bg-secondary);
    color: var(--color-text-primary);
    font-size: 14px;
    transition: all var(--transition-fast);
}

.search-box input:focus {
    outline: none;
    border-color: var(--color-primary);
    background-color: var(--color-bg-primary);
}

.search-box svg {
    position: absolute;
    left: 28px;
    top: 50%;
    transform: translateY(-50%);
    width: 16px;
    height: 16px;
    color: var(--color-text-secondary);
    pointer-events: none;
}

.notes-list {
    flex: 1;
    overflow-y: auto;
    padding: 8px;
}

.note-item {
    padding: 12px 16px;
    margin-bottom: 4px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.note-item:hover {
    background-color: var(--color-bg-secondary);
}

.note-item.active {
    background-color: var(--color-bg-secondary);
    border-left: 3px solid var(--color-primary);
    padding-left: 13px;
}

.note-item-title {
    font-size: 14px;
    font-weight: 500;
    margin-bottom: 4px;
    color: var(--color-text-primary);
}

.note-item-preview {
    font-size: 12px;
    color: var(--color-text-secondary);
    margin-bottom: 4px;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.note-item-date {
    font-size: 11px;
    color: var(--color-text-secondary);
}

.editor-container {
    flex: 1;
    display: flex;
    flex-direction: column;
    background-color: var(--color-bg-primary);
}

.welcome-view {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 40px;
}

.welcome-content {
    max-width: 600px;
    text-align: center;
}

.welcome-content h2 {
    font-size: 32px;
    font-weight: 600;
    margin-bottom: 16px;
    color: var(--color-text-primary);
}

.welcome-content p {
    font-size: 16px;
    color: var(--color-text-secondary);
    margin-bottom: 40px;
}

.feature-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 20px;
    margin-bottom: 40px;
}

.feature-card {
    background-color: var(--color-bg-secondary);
    padding: 24px;
    border-radius: var(--radius-lg);
    transition: all var(--transition-fast);
}

.feature-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.feature-card svg {
    width: 48px;
    height: 48px;
    color: var(--color-primary);
    margin-bottom: 16px;
}

.feature-card h3 {
    font-size: 16px;
    font-weight: 600;
    margin-bottom: 8px;
    color: var(--color-text-primary);
}

.feature-card p {
    font-size: 14px;
    color: var(--color-text-secondary);
    margin-bottom: 0;
}

.btn-large {
    padding: 12px 32px;
    background-color: var(--color-primary);
    color: var(--color-text-inverse);
    border: none;
    border-radius: var(--radius-md);
    font-size: 16px;
    font-weight: 500;
    cursor: pointer;
    display: inline-flex;
    align-items: center;
    gap: 12px;
    transition: all var(--transition-fast);
}

.btn-large:hover {
    background-color: var(--color-primary-hover);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-large svg {
    width: 20px;
    height: 20px;
}

.editor-view {
    flex: 1;
    display: flex;
    flex-direction: column;
}

.editor-header {
    padding: 20px 24px;
    border-bottom: 1px solid var(--color-border);
    display: flex;
    align-items: center;
    gap: 16px;
}

.note-title {
    flex: 1;
    font-size: 24px;
    font-weight: 600;
    border: none;
    background: transparent;
    color: var(--color-text-primary);
    outline: none;
}

.note-title::placeholder {
    color: var(--color-text-secondary);
}

.editor-actions {
    display: flex;
    gap: 8px;
}

.editor-content {
    flex: 1;
    display: flex;
    overflow: hidden;
}

.note-content {
    flex: 1;
    padding: 24px;
    border: none;
    background: transparent;
    color: var(--color-text-primary);
    font-size: 16px;
    line-height: 1.8;
    resize: none;
    outline: none;
}

.note-content::placeholder {
    color: var(--color-text-secondary);
}

.ai-panel {
    width: 320px;
    background-color: var(--color-bg-secondary);
    border-left: 1px solid var(--color-border);
    padding: 24px;
    overflow-y: auto;
}

.ai-panel h3 {
    font-size: 16px;
    font-weight: 600;
    margin-bottom: 16px;
    color: var(--color-text-primary);
}

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

.ai-section h4 {
    font-size: 14px;
    font-weight: 600;
    margin-bottom: 8px;
    color: var(--color-text-primary);
}

.ai-section ul {
    list-style: none;
    padding-left: 0;
}

.ai-section li {
    padding: 8px 0;
    padding-left: 20px;
    position: relative;
    font-size: 14px;
    color: var(--color-text-secondary);
}

.ai-section li::before {
    content: '•';
    position: absolute;
    left: 0;
    color: var(--color-primary);
    font-weight: bold;
}

.ai-section p {
    font-size: 14px;
    color: var(--color-text-secondary);
    line-height: 1.6;
}

@media (max-width: 768px) {
    .sidebar {
        width: 280px;
    }
    
    .ai-panel {
        display: none;
    }
    
    .feature-cards {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .sidebar {
        display: none;
    }
    
    .header-content {
        padding: 0 16px;
    }
    
    .welcome-content {
        padding: 0 16px;
    }
    
    .welcome-content h2 {
        font-size: 24px;
    }
}