:root {
    --bg-gradient-start: #667eea;
    --bg-gradient-end: #764ba2;
    --container-bg: #ffffff;
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --text-tertiary: #374151;
    --border-color: #e5e7eb;
    --step-bg: #f9fafb;
    --card-bg: #ffffff;
    --card-border: #e5e7eb;
    --card-hover-border: #667eea;
    --input-bg: #ffffff;
    --shadow-color: rgba(0, 0, 0, 0.15);
    --shadow-hover: rgba(102, 126, 234, 0.15);
    
    /* Consistent spacing scale */
    --spacing-xs: 8px;
    --spacing-sm: 12px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    --spacing-2xl: 48px;
}

body.dark-theme {
    --bg-gradient-start: #1a1a2e;
    --bg-gradient-end: #16213e;
    --container-bg: #1f2937;
    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --text-tertiary: #e5e7eb;
    --border-color: #374151;
    --step-bg: #111827;
    --card-bg: #374151;
    --card-border: #4b5563;
    --card-hover-border: #667eea;
    --input-bg: #374151;
    --shadow-color: rgba(0, 0, 0, 0.5);
    --shadow-hover: rgba(102, 126, 234, 0.3);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
}

body {
    background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
    min-height: 100vh;
    padding: var(--spacing-xl) var(--spacing-lg);
    transition: background 0.3s ease;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    background: var(--container-bg);
    border-radius: 16px;
    padding: var(--spacing-2xl);
    box-shadow: 0 20px 60px var(--shadow-color);
    transition: all 0.3s ease;
    position: relative;
}

.theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
    background: var(--step-bg);
    border: 2px solid var(--border-color);
    border-radius: 50%;
    width: 44px;
    height: 44px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s ease;
    z-index: 10;
    padding: 0;
}

.theme-toggle:hover {
    border-color: var(--card-hover-border);
    transform: scale(1.1);
    box-shadow: 0 4px 12px var(--shadow-hover);
}

.theme-toggle i {
    font-size: 1.1rem;
    color: var(--text-primary);
    transition: color 0.2s ease;
}

.header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    padding-bottom: var(--spacing-xl);
    border-bottom: 1px solid var(--border-color);
    transition: border-color 0.3s ease;
}

h1 {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
    letter-spacing: -0.02em;
    transition: color 0.3s ease;
}

.subtitle {
    font-size: 1.125rem;
    color: var(--text-secondary);
    line-height: 1.6;
    max-width: 600px;
    margin: 0 auto;
    transition: color 0.3s ease;
}

.welcome-user {
    margin-bottom: var(--spacing-md);
}

.user-greeting {
    font-size: 1.25rem;
    color: var(--card-hover-border);
    font-weight: 600;
    margin: 0;
    transition: color 0.3s ease;
}

#userNameDisplay {
    color: var(--text-primary);
    font-weight: 700;
}

button {
    width: 100%;
    padding: var(--spacing-md) var(--spacing-lg);
    border-radius: 8px;
    border: none;
    font-size: 1rem;
    font-weight: 600;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    gap: var(--spacing-sm);
    transition: all 0.2s ease;
    margin-top: var(--spacing-md);
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(102, 126, 234, 0.3);
}

button:active {
    transform: translateY(0);
}

button:disabled {
    background: var(--border-color);
    color: var(--text-secondary);
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
    opacity: 0.7;
}

.hidden {
    display: none !important;
}

/* Mobile responsive */
@media (max-width: 768px) {
    body {
        padding: var(--spacing-lg) var(--spacing-md);
    }

    .container {
        padding: var(--spacing-lg);
        padding-top: 60px;
    }

    .theme-toggle {
        top: 16px;
        right: 16px;
        width: 40px;
        height: 40px;
    }

    .theme-toggle i {
        font-size: 1rem;
    }

    h1 {
        font-size: 2rem;
    }

    .subtitle {
        font-size: 1rem;
    }
}