/* ====================================
   CSS CUSTOM PROPERTIES - PREMIUM THEME
   ==================================== */
:root {
    /* Primary Colors - Soft, modern palette */
    --primary-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --primary-color: #667eea;
    --primary-light: #8fa4f3;
    --primary-dark: #5a6fd8;
    
    /* Secondary Colors - Complementary pastels */
    --secondary-color: #f093fb;
    --secondary-light: #f5b3fc;
    --secondary-dark: #e777f8;
    
    /* Accent Colors - Bold highlights */
    --accent-color: #4ecdc4;
    --accent-secondary: #45b7b8;
    --success-color: #6c5ce7;
    --warning-color: #fdcb6e;
    
    /* Background & Surface - Clean, minimal */
    --background-color: #fafbff;
    --background-gradient: linear-gradient(135deg, #fafbff 0%, #f4f7ff 100%);
    --surface-color: #ffffff;
    --surface-elevated: #ffffff;
    --glass-effect: rgba(255, 255, 255, 0.95);
    
    /* Text Colors - High contrast, readable */
    --text-primary: #2d3748;
    --text-secondary: #718096;
    --text-muted: #a0aec0;
    --text-accent: var(--primary-color);
    
    /* Border & Dividers */
    --border-color: rgba(203, 213, 225, 0.6);
    --border-focus: var(--primary-color);
    --divider-color: rgba(203, 213, 225, 0.4);
    
    /* Shadows - Soft, modern elevation */
    --shadow-sm: 0 2px 4px rgba(16, 24, 40, 0.04);
    --shadow-md: 0 4px 12px rgba(16, 24, 40, 0.08);
    --shadow-lg: 0 8px 24px rgba(16, 24, 40, 0.12);
    --shadow-xl: 0 16px 48px rgba(16, 24, 40, 0.16);
    --shadow-glow: 0 0 20px rgba(102, 126, 234, 0.3);
    
    /* Spacing & Layout */
    --border-radius-sm: 8px;
    --border-radius: 12px;
    --border-radius-lg: 16px;
    --border-radius-xl: 24px;
    
    /* Animations & Transitions */
    --transition-fast: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-normal: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    --spring: cubic-bezier(0.68, -0.55, 0.265, 1.55);
}

/* ====================================
   DARK THEME - PREMIUM PALETTE
   ==================================== */
[data-theme="dark"] {
    /* Background & Surface - Rich, deep tones */
    --background-color: #0f0f23;
    --background-gradient: linear-gradient(135deg, #0f0f23 0%, #1a1a2e 100%);
    --surface-color: #16213e;
    --surface-elevated: #1e2749;
    --glass-effect: rgba(22, 33, 62, 0.95);
    
    /* Text Colors - High contrast for readability */
    --text-primary: #e2e8f0;
    --text-secondary: #94a3b8;
    --text-muted: #64748b;
    --text-accent: #8fa4f3;
    
    /* Accent Colors - Vibrant but not harsh */
    --accent-color: #56d1c7;
    --accent-secondary: #4dd4d6;
    
    /* Border & Dividers */
    --border-color: rgba(71, 85, 105, 0.4);
    --border-focus: var(--primary-light);
    --divider-color: rgba(71, 85, 105, 0.3);
    
    /* Shadows - Enhanced for dark theme */
    --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.4);
    --shadow-xl: 0 16px 48px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 20px rgba(143, 164, 243, 0.4);
}

/* ====================================
   RESET & BASE STYLES - PREMIUM FOUNDATION
   ==================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

*::before,
*::after {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: 'Poppins', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    font-weight: 400;
    background: var(--background-gradient);
    color: var(--text-primary);
    line-height: 1.7;
    letter-spacing: 0.01em;
    transition: var(--transition-normal);
    min-height: 100vh;
    overflow-x: hidden;
    padding-top: 80px; /* Space for fixed navbar */
}

/* ====================================
   NAVIGATION - PREMIUM MENU BAR
   ==================================== */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: var(--glass-effect);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border-color);
    z-index: 1000;
    transition: var(--transition-normal);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 80px;
}

.nav-logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    text-decoration: none;
}

.nav-logo i {
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    font-size: 1.75rem;
}

.nav-logo span {
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.02em;
}

.nav-menu {
    display: flex;
    list-style: none;
    margin: 0;
    padding: 0;
    gap: 2rem;
}

.nav-item {
    position: relative;
}

.nav-link {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.75rem 1.25rem;
    color: var(--text-secondary);
    text-decoration: none;
    border-radius: var(--border-radius);
    font-weight: 500;
    font-size: 0.95rem;
    transition: var(--transition-normal);
    position: relative;
    overflow: hidden;
}

.nav-link::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: var(--primary-gradient);
    opacity: 0;
    transition: var(--transition-normal);
    z-index: -1;
}

.nav-link:hover {
    color: white;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.nav-link:hover::before {
    left: 0;
    opacity: 1;
}

.nav-link i {
    font-size: 1rem;
    transition: var(--transition-fast);
}

.nav-link:hover i {
    transform: scale(1.1);
}

/* Theme toggle in navbar */
.navbar .theme-toggle {
    position: static;
    margin: 0;
}

/* ====================================
   LAYOUT - PREMIUM CONTAINER SYSTEM
   ==================================== */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    position: relative;
}

/* ====================================
   HEADER - PREMIUM BRANDING
   ==================================== */
header {
    text-align: center;
    margin-bottom: 4rem;
    margin-top: 2rem;
    position: relative;
    z-index: 10;
}

header h1 {
    font-size: clamp(2.5rem, 6vw, 4rem);
    font-weight: 700;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 1rem;
    letter-spacing: -0.02em;
    line-height: 1.1;
}

header h1 i {
    margin-right: 0.75rem;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    animation: float 3s ease-in-out infinite;
    display: inline-block;
}

header p {
    font-size: 1.25rem;
    font-weight: 400;
    color: var(--text-secondary);
    margin-bottom: 2rem;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
    line-height: 1.6;
}

/* ====================================
   THEME TOGGLE - PREMIUM FLOATING BUTTON
   ==================================== */
.theme-toggle {
    background: var(--glass-effect);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: 50%;
    width: 56px;
    height: 56px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition-normal);
    box-shadow: var(--shadow-md);
    z-index: 100;
}

.theme-toggle:hover {
    transform: translateY(-2px) scale(1.05);
    box-shadow: var(--shadow-lg);
    border-color: var(--border-focus);
}

.theme-toggle:active {
    transform: translateY(-1px) scale(1.02);
}

.theme-toggle i {
    font-size: 1.25rem;
    color: var(--text-accent);
    transition: var(--transition-fast);
}

.theme-toggle:hover i {
    transform: rotate(180deg);
    color: var(--primary-color);
}

/* ====================================
   CALCULATOR CONTAINER - PREMIUM CARD
   ==================================== */
.calculator-container {
    background: var(--glass-effect);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-xl);
    padding: 3rem;
    box-shadow: var(--shadow-xl);
    margin-bottom: 3rem;
    flex: 1;
    position: relative;
    overflow: hidden;
}

.calculator-container::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 1px;
    background: linear-gradient(90deg, transparent, var(--primary-color), transparent);
    opacity: 0.5;
}

/* ====================================
   INPUT SECTION - PREMIUM FORM ELEMENTS
   ==================================== */
.input-section {
    margin-bottom: 3rem;
}

.pet-selection {
    margin-bottom: 2rem;
}

.pet-selection label {
    display: block;
    margin-bottom: 0.75rem;
    font-weight: 600;
    font-size: 1.1rem;
    color: var(--text-primary);
    letter-spacing: 0.01em;
}

.pet-dropdown {
    width: 100%;
    padding: 1.25rem 1.5rem;
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius-lg);
    background: var(--surface-color);
    color: var(--text-primary);
    font-size: 1rem;
    font-family: inherit;
    font-weight: 500;
    transition: var(--transition-normal);
    cursor: pointer;
    box-shadow: var(--shadow-sm);
}

.pet-dropdown:focus {
    outline: none;
    border-color: var(--border-focus);
    box-shadow: var(--shadow-md), 0 0 0 4px rgba(102, 126, 234, 0.1);
    transform: translateY(-1px);
}

.pet-dropdown:hover {
    border-color: var(--primary-light);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.pet-dropdown option {
    padding: 0.75rem;
    font-weight: 500;
}

.pet-dropdown optgroup {
    font-weight: 700;
    color: var(--primary-color);
    font-size: 0.95rem;
    padding: 0.5rem;
}

/* ====================================
   AGE INPUT SECTION - PREMIUM CONTROLS
   ==================================== */
.age-input-section {
    margin-bottom: 2rem;
}

.input-mode-toggle {
    display: flex;
    margin-bottom: 1.5rem;
    background: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-lg);
    padding: 0.25rem;
    box-shadow: var(--shadow-sm);
}

.mode-btn {
    flex: 1;
    padding: 0.875rem 1.5rem;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition-normal);
    font-weight: 600;
    font-size: 0.95rem;
    letter-spacing: 0.01em;
}

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

.mode-btn.active {
    background: var(--primary-gradient);
    color: white;
    box-shadow: var(--shadow-sm);
    transform: translateY(-1px);
}

.age-input {
    display: flex;
    align-items: center;
    gap: 1.5rem;
}

.age-input label {
    font-weight: 600;
    font-size: 1.1rem;
    color: var(--text-primary);
    min-width: 100px;
    letter-spacing: 0.01em;
}

.age-input input {
    flex: 1;
    padding: 1.25rem 1.5rem;
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius-lg);
    background: var(--surface-color);
    color: var(--text-primary);
    font-size: 1.1rem;
    font-family: inherit;
    font-weight: 500;
    transition: var(--transition-normal);
    box-shadow: var(--shadow-sm);
}

.age-input input:focus {
    outline: none;
    border-color: var(--border-focus);
    box-shadow: var(--shadow-md), 0 0 0 4px rgba(102, 126, 234, 0.1);
    transform: translateY(-1px);
}

.age-input input:hover {
    border-color: var(--primary-light);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.unit-label {
    font-weight: 600;
    font-size: 1rem;
    color: var(--text-secondary);
    min-width: 80px;
    letter-spacing: 0.01em;
}

/* ====================================
   BUTTON GROUP - PREMIUM ACTION BUTTONS
   ==================================== */
.button-group {
    display: flex;
    gap: 1.5rem;
    flex-wrap: wrap;
    margin-top: 2rem;
}

.calculate-btn,
.random-btn {
    flex: 1;
    min-width: 180px;
    padding: 1.25rem 2rem;
    border: none;
    border-radius: var(--border-radius-lg);
    cursor: pointer;
    font-size: 1.1rem;
    font-weight: 600;
    font-family: inherit;
    letter-spacing: 0.01em;
    transition: var(--transition-normal);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.75rem;
    position: relative;
    overflow: hidden;
    box-shadow: var(--shadow-md);
}

.calculate-btn {
    background: var(--primary-gradient);
    color: white;
    border: 2px solid transparent;
}

.calculate-btn:hover {
    transform: translateY(-3px) scale(1.02);
    box-shadow: var(--shadow-glow);
}

.calculate-btn:active {
    transform: translateY(-1px) scale(1.01);
}

.random-btn {
    background: linear-gradient(135deg, var(--accent-color) 0%, var(--accent-secondary) 100%);
    color: white;
    border: 2px solid transparent;
}

.random-btn:hover {
    transform: translateY(-3px) scale(1.02);
    box-shadow: 0 0 20px rgba(78, 205, 196, 0.4);
}

.random-btn:active {
    transform: translateY(-1px) scale(1.01);
}

/* Button icon animations */
.calculate-btn i,
.random-btn i {
    transition: var(--transition-fast);
}

.calculate-btn:hover i {
    transform: rotate(360deg);
}

.random-btn:hover i {
    transform: scale(1.2) rotate(180deg);
}

/* ====================================
   RESULT SECTION - PREMIUM DISPLAY
   ==================================== */
.result-section {
    text-align: center;
    padding: 3rem 0;
    position: relative;
}

.pet-image-container {
    margin-bottom: 3rem;
    position: relative;
}

.pet-image {
    width: 180px;
    height: 180px;
    margin: 0 auto;
    border-radius: 50%;
    background: var(--primary-gradient);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 4rem;
    transition: var(--transition-slow);
    box-shadow: var(--shadow-xl);
    position: relative;
    overflow: hidden;
}

.pet-image::before {
    content: '';
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: linear-gradient(45deg, transparent 30%, rgba(255, 255, 255, 0.2) 50%, transparent 70%);
    transform: rotate(45deg);
    transition: var(--transition-slow);
}

.pet-image:hover {
    transform: scale(1.05) rotate(5deg);
    box-shadow: var(--shadow-glow);
}

.pet-image:hover::before {
    animation: shimmer 2s ease-in-out;
}

.pet-image.has-emoji {
    font-size: 5rem;
    background: var(--glass-effect);
    border: 3px solid var(--border-color);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
}

.result-display {
    margin-bottom: 2rem;
    opacity: 0;
    transform: translateY(20px);
    transition: var(--transition-slow);
}

.result-display.show {
    opacity: 1;
    transform: translateY(0);
}

.result-display h2 {
    font-size: clamp(1.75rem, 5vw, 3rem);
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 1.5rem;
    line-height: 1.2;
    letter-spacing: -0.02em;
}

.result-display .age-result {
    font-size: clamp(1.5rem, 4vw, 2.25rem);
    font-weight: 700;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    background-color: var(--primary-color); /* Fallback */
    color: var(--primary-color); /* Fallback */
    padding: 1.5rem;
    border-radius: var(--border-radius-lg);
    margin-top: 1.5rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
    background-attachment: fixed;
}

.fun-fact {
    background: var(--glass-effect);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-left: 4px solid var(--secondary-color);
    padding: 1.5rem;
    border-radius: var(--border-radius-lg);
    margin-top: 2rem;
    font-style: italic;
    font-size: 1.1rem;
    color: var(--text-secondary);
    line-height: 1.6;
    box-shadow: var(--shadow-md);
    opacity: 0;
    transform: translateY(20px);
    transition: var(--transition-slow);
}

.fun-fact.show {
    opacity: 1;
    transform: translateY(0);
}

.fun-fact::before {
    content: "💡 Fun Fact: ";
    font-weight: 700;
    font-style: normal;
    color: var(--secondary-color);
    font-size: 1rem;
}

/* ====================================
   FOOTER - PREMIUM BRANDING
   ==================================== */
footer {
    text-align: center;
    padding: 3rem 0 2rem;
    color: var(--text-muted);
    border-top: 1px solid var(--divider-color);
    margin-top: auto;
    position: relative;
}

footer::before {
    content: '';
    position: absolute;
    top: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 100px;
    height: 1px;
    background: var(--primary-gradient);
}

footer p {
    font-size: 0.95rem;
    font-weight: 400;
    letter-spacing: 0.02em;
}

footer i {
    color: var(--accent-color);
    animation: heartbeat 2s ease-in-out infinite;
}

/* ====================================
   ANIMATIONS - PREMIUM MOTION DESIGN
   ==================================== */

/* Floating animation for header icon */
@keyframes float {
    0%, 100% {
        transform: translateY(0px);
    }
    50% {
        transform: translateY(-10px);
    }
}

/* Shimmer effect for pet images */
@keyframes shimmer {
    0% {
        transform: translateX(-100%) rotate(45deg);
    }
    100% {
        transform: translateX(200%) rotate(45deg);
    }
}

/* Heartbeat animation for footer heart */
@keyframes heartbeat {
    0%, 50%, 100% {
        transform: scale(1);
    }
    25%, 75% {
        transform: scale(1.1);
    }
}

/* Fade in animation for results */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Scale in animation */
@keyframes scaleIn {
    from {
        opacity: 0;
        transform: scale(0.8);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

/* Pulse animation for loading states */
@keyframes pulse {
    0%, 100% {
        opacity: 1;
    }
    50% {
        opacity: 0.5;
    }
}

/* Spin animation for loading */
@keyframes spin {
    to {
        transform: rotate(360deg);
    }
}

/* Utility animation classes */
.fade-in {
    animation: fadeInUp 0.6s var(--spring);
}

.scale-in {
    animation: scaleIn 0.4s var(--spring);
}

.pulse {
    animation: pulse 2s ease-in-out infinite;
}

/* ====================================
   RESPONSIVE DESIGN - PREMIUM MOBILE FIRST
   ==================================== */
@media (max-width: 768px) {
    .nav-container {
        padding: 0 1.5rem;
        height: 70px;
    }
    
    .nav-logo {
        font-size: 1.25rem;
    }
    
    .nav-logo i {
        font-size: 1.5rem;
    }
    
    .nav-menu {
        gap: 1rem;
    }
    
    .nav-link {
        padding: 0.5rem 0.75rem;
        font-size: 0.9rem;
    }
    
    .nav-link span {
        display: none;
    }
    
    .nav-link i {
        font-size: 1.1rem;
    }
    
    .navbar .theme-toggle {
        width: 48px;
        height: 48px;
    }
    
    body {
        padding-top: 70px;
    }
    
    .container {
        padding: 1.5rem;
    }
    
    .calculator-container {
        padding: 2rem;
        border-radius: var(--border-radius-lg);
        margin-bottom: 2rem;
    }
    
    .theme-toggle {
        position: static;
        margin: 1.5rem auto 0;
    }
    
    header {
        margin-bottom: 3rem;
    }
    
    header h1 {
        font-size: clamp(2rem, 8vw, 3rem);
    }
    
    .age-input {
        flex-direction: column;
        align-items: stretch;
        gap: 1rem;
    }
    
    .age-input label {
        min-width: auto;
        text-align: center;
    }
    
    .unit-label {
        text-align: center;
        min-width: auto;
    }
    
    .button-group {
        flex-direction: column;
        gap: 1rem;
    }
    
    .calculate-btn,
    .random-btn {
        min-width: auto;
        padding: 1rem 1.5rem;
    }
    
    .pet-image {
        width: 140px;
        height: 140px;
        font-size: 3rem;
    }
    
    .pet-image.has-emoji {
        font-size: 4rem;
    }
    
    .result-section {
        padding: 2rem 0;
    }
}

@media (max-width: 480px) {
    .nav-container {
        padding: 0 1rem;
        height: 60px;
    }
    
    .nav-logo {
        font-size: 1.1rem;
    }
    
    .nav-logo i {
        font-size: 1.3rem;
    }
    
    .nav-menu {
        gap: 0.5rem;
    }
    
    .nav-link {
        padding: 0.4rem 0.5rem;
    }
    
    .navbar .theme-toggle {
        width: 44px;
        height: 44px;
    }
    
    body {
        padding-top: 60px;
    }
    
    .container {
        padding: 1rem;
    }
    
    .calculator-container {
        padding: 1.5rem;
        border-radius: var(--border-radius);
    }
    
    header {
        margin-bottom: 2rem;
    }
    
    .pet-image {
        width: 120px;
        height: 120px;
        font-size: 2.5rem;
    }
    
    .pet-image.has-emoji {
        font-size: 3.5rem;
    }
    
    .pet-dropdown,
    .age-input input {
        padding: 1rem;
        font-size: 0.95rem;
    }
    
    .calculate-btn,
    .random-btn {
        padding: 0.875rem 1.25rem;
        font-size: 1rem;
    }
}

/* ====================================
   STATES - ERROR AND LOADING PREMIUM STYLES
   ==================================== */
.error {
    border-color: var(--warning-color) !important;
    box-shadow: var(--shadow-md), 0 0 0 4px rgba(253, 203, 110, 0.2) !important;
    animation: shake 0.5s ease-in-out;
}

.error-message {
    color: var(--warning-color);
    font-size: 0.9rem;
    font-weight: 500;
    margin-top: 0.75rem;
    display: block;
    padding: 0.5rem 1rem;
    background: rgba(253, 203, 110, 0.1);
    border-radius: var(--border-radius);
    border-left: 3px solid var(--warning-color);
}

/* Loading state */
.loading {
    opacity: 0.6;
    pointer-events: none;
    position: relative;
}

.loading::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 24px;
    height: 24px;
    margin: -12px 0 0 -12px;
    border: 3px solid var(--border-color);
    border-radius: 50%;
    border-top-color: var(--primary-color);
    animation: spin 1s linear infinite;
}

/* Shake animation for errors */
@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}