:root {
    /* Color Palette */
    --primary-hue: 260;
    --secondary-hue: 200;
    --accent-hue: 320;

    --bg-dark: hsl(240, 15%, 8%);
    --bg-card: hsla(240, 15%, 12%, 0.8);
    --bg-input: hsla(240, 15%, 18%, 0.6);

    --primary: hsl(var(--primary-hue), 70%, 60%);
    --primary-light: hsl(var(--primary-hue), 70%, 70%);
    --secondary: hsl(var(--secondary-hue), 65%, 55%);
    --accent: hsl(var(--accent-hue), 75%, 65%);

    --text-primary: hsl(0, 0%, 95%);
    --text-secondary: hsl(0, 0%, 70%);
    --text-muted: hsl(0, 0%, 50%);

    --gradient-1: linear-gradient(135deg, var(--primary), var(--secondary));
    --gradient-2: linear-gradient(135deg, var(--secondary), var(--accent));
    --gradient-3: linear-gradient(135deg, var(--accent), var(--primary));

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;

    /* Border Radius */
    --radius-sm: 0.5rem;
    --radius-md: 1rem;
    --radius-lg: 1.5rem;

    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-dark);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    overflow-x: hidden;
}

/* Animated Background */
body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background:
        radial-gradient(circle at 20% 30%, hsla(var(--primary-hue), 70%, 50%, 0.15) 0%, transparent 50%),
        radial-gradient(circle at 80% 70%, hsla(var(--secondary-hue), 65%, 50%, 0.15) 0%, transparent 50%),
        radial-gradient(circle at 50% 50%, hsla(var(--accent-hue), 75%, 50%, 0.1) 0%, transparent 50%);
    z-index: -1;
    animation: backgroundPulse 15s ease-in-out infinite;
}

@keyframes backgroundPulse {

    0%,
    100% {
        opacity: 1;
    }

    50% {
        opacity: 0.7;
    }
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-lg);
}

/* Header */
header {
    text-align: center;
    padding: var(--spacing-xl) 0;
    margin-bottom: var(--spacing-lg);
}

h1 {
    font-size: clamp(2rem, 5vw, 3.5rem);
    font-weight: 800;
    background: var(--gradient-1);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-sm);
    animation: fadeInDown 0.8s ease;
}

.subtitle {
    font-size: clamp(1rem, 2vw, 1.25rem);
    color: var(--text-secondary);
    animation: fadeInUp 0.8s ease;
}

/* Card Styling */
.card {
    background: var(--bg-card);
    backdrop-filter: blur(20px);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    border: 1px solid hsla(0, 0%, 100%, 0.1);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
    animation: fadeIn 0.6s ease;
}

/* Form Styling */
.input-section {
    margin-bottom: var(--spacing-xl);
}

.form-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-md);
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

label {
    font-weight: 600;
    color: var(--text-secondary);
    font-size: 0.9rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

input,
select {
    background: var(--bg-input);
    border: 2px solid hsla(0, 0%, 100%, 0.1);
    border-radius: var(--radius-sm);
    padding: var(--spacing-sm);
    color: var(--text-primary);
    font-size: 1rem;
    transition: all var(--transition-normal);
    font-family: inherit;
}

input:focus,
select:focus {
    outline: none;
    border-color: var(--primary);
    background: var(--bg-card);
    box-shadow: 0 0 0 3px hsla(var(--primary-hue), 70%, 60%, 0.2);
}

input::placeholder {
    color: var(--text-muted);
}

select option {
    background: var(--bg-dark);
    color: var(--text-primary);
}

/* Button Styling */
.btn {
    background: var(--gradient-1);
    color: white;
    border: none;
    padding: var(--spacing-sm) var(--spacing-lg);
    border-radius: var(--radius-sm);
    font-size: 1.1rem;
    font-weight: 700;
    cursor: pointer;
    transition: all var(--transition-normal);
    text-transform: uppercase;
    letter-spacing: 1px;
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 15px hsla(var(--primary-hue), 70%, 50%, 0.4);
}

.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.3), transparent);
    transition: left var(--transition-slow);
}

.btn:hover::before {
    left: 100%;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px hsla(var(--primary-hue), 70%, 50%, 0.6);
}

.btn:active {
    transform: translateY(0);
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
}

/* API Key Section */
.api-key-section {
    background: var(--bg-input);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    margin-bottom: var(--spacing-md);
    border: 1px solid hsla(var(--accent-hue), 75%, 65%, 0.3);
}

.api-key-section p {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-sm);
    font-size: 0.9rem;
}

.api-key-section a {
    color: var(--accent);
    text-decoration: none;
    font-weight: 600;
    transition: color var(--transition-fast);
}

.api-key-section a:hover {
    color: var(--primary-light);
    text-decoration: underline;
}

/* Loading State */
.loading {
    text-align: center;
    padding: var(--spacing-xl);
}

.spinner {
    width: 50px;
    height: 50px;
    margin: 0 auto var(--spacing-md);
    border: 4px solid hsla(0, 0%, 100%, 0.1);
    border-top: 4px solid var(--primary);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

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

    100% {
        transform: rotate(360deg);
    }
}

/* Timeline Styling */
.timeline {
    position: relative;
    padding: var(--spacing-lg) 0;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 50%;
    top: 0;
    bottom: 0;
    width: 3px;
    background: var(--gradient-1);
    transform: translateX(-50%);
}

.timeline-item {
    position: relative;
    margin-bottom: var(--spacing-xl);
    animation: fadeInUp 0.6s ease backwards;
}

.timeline-item:nth-child(1) {
    animation-delay: 0.1s;
}

.timeline-item:nth-child(2) {
    animation-delay: 0.3s;
}

.timeline-item:nth-child(3) {
    animation-delay: 0.5s;
}

.timeline-content {
    background: var(--bg-card);
    backdrop-filter: blur(20px);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    border: 1px solid hsla(0, 0%, 100%, 0.1);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
    position: relative;
    width: calc(50% - 40px);
    transition: all var(--transition-normal);
}

.timeline-content:hover {
    transform: translateY(-5px);
    box-shadow: 0 12px 40px rgba(0, 0, 0, 0.4);
    border-color: hsla(0, 0%, 100%, 0.2);
}

.timeline-item:nth-child(odd) .timeline-content {
    margin-left: auto;
    margin-right: 40px;
}

.timeline-item:nth-child(even) .timeline-content {
    margin-left: 40px;
}

.timeline-marker {
    position: absolute;
    left: 50%;
    top: 30px;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background: var(--gradient-2);
    border: 4px solid var(--bg-dark);
    transform: translateX(-50%);
    z-index: 1;
    box-shadow: 0 0 0 4px hsla(var(--secondary-hue), 65%, 55%, 0.3);
    animation: pulse 2s ease-in-out infinite;
}

@keyframes pulse {

    0%,
    100% {
        box-shadow: 0 0 0 4px hsla(var(--secondary-hue), 65%, 55%, 0.3);
    }

    50% {
        box-shadow: 0 0 0 8px hsla(var(--secondary-hue), 65%, 55%, 0.1);
    }
}

.stage-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-sm);
    border-bottom: 2px solid hsla(0, 0%, 100%, 0.1);
}

.stage-title {
    font-size: 1.5rem;
    font-weight: 700;
    background: var(--gradient-2);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stage-years {
    color: var(--text-secondary);
    font-weight: 600;
    font-size: 1.1rem;
}

.stage-age {
    color: var(--text-muted);
    font-size: 0.9rem;
    margin-bottom: var(--spacing-sm);
}

.stage-summary {
    color: var(--text-primary);
    line-height: 1.8;
    font-size: 1rem;
}

.stage-summary p {
    margin-bottom: var(--spacing-sm);
}

/* Error Styling */
.error {
    background: hsla(0, 70%, 50%, 0.1);
    border: 2px solid hsla(0, 70%, 50%, 0.5);
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
    color: hsl(0, 70%, 70%);
    margin-top: var(--spacing-md);
    animation: shake 0.5s ease;
}

@keyframes shake {

    0%,
    100% {
        transform: translateX(0);
    }

    25% {
        transform: translateX(-10px);
    }

    75% {
        transform: translateX(10px);
    }
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Responsive Design */
@media (max-width: 768px) {
    .timeline::before {
        left: 20px;
    }

    .timeline-content {
        width: calc(100% - 60px);
        margin-left: 60px !important;
        margin-right: 0 !important;
    }

    .timeline-marker {
        left: 20px;
    }

    .form-grid {
        grid-template-columns: 1fr;
    }

    .stage-header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-xs);
    }
}

/* Hidden Class */
.hidden {
    display: none;
}