/* Core CSS Variables */
:root {
    /* Colors */
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --primary-light: #dbeafe;
    --secondary-color: #64748b;
    --secondary-hover: #475569;
    --accent-color: #10b981;
    --accent-hover: #059669;
    --selected-color: #047857;
    --selected-bg: #d1fae5;
    
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --text-light: #9ca3af;
    --text-other-month: #a1a1aa;
    --text-white: #ffffff;
    
    --background-primary: #ffffff;
    --background-secondary: #e5e7eb;
    --background-tertiary: #f1f5f9;
    --background-entry: #ededf5;
    --background-dark: #1f2937;
    --background-weekend: #e5e7eb;
    --background-other-month: #d1d5db;
    --background-button: #60a5fa;
    --background-button-disabled: #d1d5db;
    --text-disabled: #c4c4c4;
    --border-disabled: #d1d5db;
    --modal-backdrop: rgba(0, 0, 0, 0.6);
    --focus-shadow: rgba(59, 130, 246, 0.1);
    
    --border-color: #e5e7eb;
    --border-light: #f3f4f6;
    --border-focus: #3b82f6;
    
    --error-color: #ef4444;
    --error-bg: #fef2f2;
    --success-color: #10b981;
    --success-bg: #f0fdf4;
    --warning-color: #f59e0b;
    --warning-bg: #fffbeb;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    
    /* Borders */
    --border-radius-sm: 4px;
    --border-radius-md: 8px;
    --border-radius-lg: 12px;
    --border-radius-xl: 16px;
    --border-radius-full: 9999px;
    
    --border-width-thin: 1px;
    --border-width-medium: 2px;
    --border-width-thick: 3px;
    
    /* Typography */
    --font-family-primary: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Arial, sans-serif;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 1.875rem;
    --font-size-4xl: 2.25rem;
    
    /* Spacing */
    --spacing-xs: 0.1rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    --spacing-3xl: 4rem;
    
    /* Transitions */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-family-primary);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--background-primary);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* App Container */
#app-container {
    min-height: 100vh;
    position: relative;
}

#page-container {
    min-height: 100vh;
    position: relative;
}

/* Loading Overlay */
.loading-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(255, 255, 255, 0.9);
    display: flex;
    justify-content: center;
    align-items: center;
    opacity: 0;
    visibility: hidden;
    transition: opacity var(--transition-normal), visibility var(--transition-normal);
}

.loading-overlay.show {
    opacity: 1;
    visibility: visible;
}

.loading-spinner {
    width: 40px;
    height: 40px;
    border: 3px solid var(--border-light);
    border-top: 3px solid var(--primary-color);
    border-radius: var(--border-radius-full);
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Button Styles */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-xs) var(--spacing-lg);
    border: var(--border-width-thin) solid transparent;
    border-radius: var(--border-radius-lg);
    font-size: var(--font-size-base);
    font-weight: 500;
    text-decoration: none;
    cursor: pointer;
    transition: all var(--transition-fast);
    outline: none;
    position: relative;
    user-select: none;
}

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

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

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

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

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

.btn-ghost {
    background-color: transparent;
    color: var(--text-secondary);
}

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

.btn:disabled {
    cursor: not-allowed;
    background-color: var(--background-button-disabled);
    color: var(--text-disabled);
    border-color: var(--border-disabled);
}

.btn:disabled:hover {
    background-color: var(--background-button-disabled);
    color: var(--text-disabled);
    transform: none;
}

#logout-btn {
    padding: calc(var(--spacing-xs) * 5) var(--spacing-lg);
    margin-right: var(--spacing-sm);
}

/* Form Styles */
.form-group {
    margin-bottom: var(--spacing-lg);
}

.form-label {
    display: block;
    margin-bottom: var(--spacing-sm);
    font-weight: 500;
    color: var(--text-primary);
}

.form-input {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    border: var(--border-width-thin) solid var(--border-color);
    border-radius: var(--border-radius-md);
    font-size: var(--font-size-base);
    background-color: var(--background-primary);
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.form-input:focus {
    outline: none;
    border-color: var(--border-focus);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.form-input.error {
    border-color: var(--error-color);
}

.form-error {
    margin-top: var(--spacing-xs);
    font-size: var(--font-size-sm);
    color: var(--error-color);
}

/* Card Styles */
.card {
    background-color: var(--background-primary);
    border: var(--border-width-thin) solid var(--border-color);
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
}

.card-header {
    border-bottom: var(--border-width-thin) solid var(--border-color);
    text-align: center;
}

.card-body {
    padding: var(--spacing-lg);
}

.card-footer {
    padding: var(--spacing-lg);
    border-top: var(--border-width-thin) solid var(--border-color);
    background-color: var(--background-secondary);
}

/* Utility Classes */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.mt-xs { margin-top: var(--spacing-xs); }
.mt-sm { margin-top: var(--spacing-sm); }
.mt-md { margin-top: var(--spacing-md); }
.mt-lg { margin-top: var(--spacing-lg); }
.mt-xl { margin-top: var(--spacing-xl); }

.mb-xs { margin-bottom: var(--spacing-xs); }
.mb-sm { margin-bottom: var(--spacing-sm); }
.mb-md { margin-bottom: var(--spacing-md); }
.mb-lg { margin-bottom: var(--spacing-lg); }
.mb-xl { margin-bottom: var(--spacing-xl); }

.hidden { display: none !important; }
.invisible { visibility: hidden; }

/* Responsive Design */
@media (max-width: 768px) {
    .btn {
        padding: var(--spacing-md) var(--spacing-lg);
        font-size: var(--font-size-sm);
        }
    
    .card-body,
    .card-footer {
        padding: var(--spacing-md);
    }
}