/* Default / dark theme */
:root,
html[data-theme="dark"] {
    /* Color Palette */
    --bg-main: #0a0b10;
    --bg-surface: rgba(255, 255, 255, 0.03);
    --bg-surface-hover: rgba(255, 255, 255, 0.06);
    --border-color: rgba(255, 255, 255, 0.1);
    
    --text-primary: #f8f9fa;
    --text-secondary: #adb5bd;
    --text-accent: #66b2ff;
    --text-snellen: #ffffff;
    --text-snellen-shadow: rgba(59, 130, 246, 0.5);
    --code-text: #a78bfa;
    --code-bg: rgba(0, 0, 0, 0.4);
    --code-border: rgba(167, 139, 250, 0.2);
    --input-bg: rgba(0, 0, 0, 0.2);
    --input-bg-focus: rgba(0, 0, 0, 0.4);
    --placeholder: rgba(255, 255, 255, 0.2);
    --logic-box-bg: rgba(0, 0, 0, 0.2);
    --details-border: rgba(255, 255, 255, 0.05);
    --primary-result-bg: rgba(59, 130, 246, 0.1);
    --primary-result-border: rgba(59, 130, 246, 0.2);
    --glow-1: rgba(59, 130, 246, 0.08);
    --glow-2: rgba(139, 92, 246, 0.08);
    --icon-link-bg: rgba(255, 255, 255, 0.05);
    --icon-link-border: rgba(255, 255, 255, 0.12);
    --dialog-surface: #14151c;
    --submit-shadow: rgba(59, 130, 246, 0.2);
    --submit-shadow-hover: rgba(59, 130, 246, 0.3);
    --card-shadow: rgba(0, 0, 0, 0.2);
    --select-option-bg: var(--bg-main);
    
    --brand-gradient: linear-gradient(135deg, #3b82f6, #8b5cf6);
    --brand-gradient-hover: linear-gradient(135deg, #2563eb, #7c3aed);
    
    --error-color: #ff6b6b;
    --focus-ring: 0 0 0 3px rgba(59, 130, 246, 0.5);

    /* Spacing & Radii */
    --radius-md: 12px;
    --radius-lg: 16px;
    --spacing-sm: 8px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    
    /* Typography */
    --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
    --font-mono: 'Roboto Mono', monospace;
    
    /* Animations */
    --transition-fast: 0.2s ease;
    --transition-smooth: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

html[data-theme="light"] {
    --bg-main: #f4f6f9;
    --bg-surface: rgba(255, 255, 255, 0.9);
    --bg-surface-hover: rgba(255, 255, 255, 0.95);
    --border-color: rgba(15, 23, 42, 0.1);

    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-accent: #2563eb;
    --text-snellen: #1e3a5f;
    --text-snellen-shadow: rgba(37, 99, 235, 0.25);
    --code-text: #5b21b6;
    --code-bg: rgba(15, 23, 42, 0.06);
    --code-border: rgba(91, 33, 182, 0.2);
    --input-bg: rgba(255, 255, 255, 0.8);
    --input-bg-focus: #ffffff;
    --placeholder: rgba(15, 23, 42, 0.35);
    --logic-box-bg: rgba(15, 23, 42, 0.04);
    --details-border: rgba(15, 23, 42, 0.08);
    --primary-result-bg: rgba(37, 99, 235, 0.08);
    --primary-result-border: rgba(37, 99, 235, 0.2);
    --glow-1: rgba(37, 99, 235, 0.06);
    --glow-2: rgba(124, 58, 237, 0.06);
    --icon-link-bg: rgba(255, 255, 255, 0.7);
    --icon-link-border: rgba(15, 23, 42, 0.1);
    --dialog-surface: #ffffff;
    --submit-shadow: rgba(37, 99, 235, 0.2);
    --submit-shadow-hover: rgba(37, 99, 235, 0.28);
    --card-shadow: rgba(15, 23, 42, 0.08);
    --select-option-bg: #ffffff;

    --brand-gradient: linear-gradient(135deg, #2563eb, #7c3aed);
    --brand-gradient-hover: linear-gradient(135deg, #1d4ed8, #6d28d9);
    --focus-ring: 0 0 0 3px rgba(37, 99, 235, 0.4);
    --error-color: #dc2626;
}

/* Screen reader only utility class */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
}

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

body {
    background-color: var(--bg-main);
    color: var(--text-primary);
    font-family: var(--font-sans);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: var(--spacing-md);
    padding-top: max(var(--spacing-md), 56px);
    background-image: 
        radial-gradient(circle at 15% 50%, var(--glow-1), transparent 25%),
        radial-gradient(circle at 85% 30%, var(--glow-2), transparent 25%);
    transition: background-color var(--transition-smooth), color var(--transition-smooth);
}

.top-bar {
    position: fixed;
    top: 0;
    inset-inline-end: 0;
    z-index: 10;
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: flex-end;
    gap: var(--spacing-sm);
    padding-block-start: max(var(--spacing-sm), env(safe-area-inset-top, 0px));
    padding-block-end: var(--spacing-sm);
    padding-inline-end: max(var(--spacing-md), env(safe-area-inset-right, 0px));
    padding-inline-start: max(var(--spacing-md), env(safe-area-inset-left, 0px));
}

.lang-switcher {
    display: flex;
    align-items: center;
}

/* Wrapper hides native select chrome glitches (e.g. repeated arrows in RTL). */
.lang-switcher__field {
    position: relative;
    display: inline-flex;
    align-items: stretch;
}

.lang-switcher__field::after {
    content: "";
    position: absolute;
    inset-inline-end: 0.65rem;
    top: 50%;
    width: 0;
    height: 0;
    margin-top: -0.125rem;
    border-inline-start: 4px solid transparent;
    border-inline-end: 4px solid transparent;
    border-block-start: 5px solid var(--text-secondary);
    pointer-events: none;
}

.lang-switcher__select {
    min-width: 7.5rem;
    max-width: 11rem;
    height: 40px;
    padding-block: 0;
    padding-inline-start: var(--spacing-sm);
    padding-inline-end: 1.75rem;
    border-radius: var(--radius-md);
    font: inherit;
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-primary);
    background-color: var(--icon-link-bg);
    border: 1px solid var(--icon-link-border);
    box-shadow: 0 1px 3px var(--card-shadow);
    cursor: pointer;
    transition: background-color var(--transition-fast), color var(--transition-fast), border-color var(--transition-fast);
    appearance: none;
    -webkit-appearance: none;
    -moz-appearance: none;
}

.lang-switcher__select:hover {
    background-color: var(--bg-surface-hover);
    border-color: var(--text-accent);
    color: var(--text-accent);
}

.lang-switcher__field:hover::after {
    border-block-start-color: var(--text-accent);
}

.lang-switcher__select:focus {
    outline: none;
    box-shadow: var(--focus-ring);
}

a.icon-link,
button.icon-link {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    border-radius: var(--radius-md);
    color: var(--text-primary);
    text-decoration: none;
    background: var(--icon-link-bg);
    border: 1px solid var(--icon-link-border);
    box-shadow: 0 1px 3px var(--card-shadow);
    transition: background var(--transition-fast), color var(--transition-fast), border-color var(--transition-fast), transform var(--transition-fast);
    font: inherit;
    cursor: pointer;
}

a.icon-link:hover,
button.icon-link:hover {
    background: var(--bg-surface-hover);
    border-color: var(--text-accent);
    color: var(--text-accent);
}

a.icon-link:focus,
button.icon-link:focus {
    outline: none;
    box-shadow: var(--focus-ring);
}

.icon-link__icon {
    display: inline-flex;
    line-height: 0;
    position: relative;
}

.icon-link__icon .theme-icon {
    display: block;
}

/* Dark mode: show sun (switch to light); light mode: show moon (switch to dark) */
html[data-theme="dark"] .theme-icon--moon {
    display: none;
}
html[data-theme="light"] .theme-icon--sun {
    display: none;
}
html[data-theme="light"] .theme-icon--moon {
    display: block;
}

/* Disclaimer dialog (native) */
.disclaimer-dialog {
    margin: auto;
    max-width: 28rem;
    width: min(calc(100% - 2rem), 28rem);
    padding: var(--spacing-lg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    background: var(--dialog-surface);
    color: var(--text-primary);
    box-shadow: 0 20px 50px var(--card-shadow);
    line-height: 1.55;
}

.disclaimer-dialog::backdrop {
    background: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(2px);
}

html[data-theme="light"] .disclaimer-dialog::backdrop {
    background: rgba(15, 23, 42, 0.35);
}

.disclaimer-dialog h2 {
    font-size: 1.2rem;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.disclaimer-dialog p {
    margin-bottom: var(--spacing-md);
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.disclaimer-dialog p strong {
    color: var(--text-primary);
}

.disclaimer-dialog__actions {
    margin-top: var(--spacing-md);
    margin-bottom: 0;
}

.disclaimer-accept {
    width: 100%;
    background: var(--brand-gradient);
    color: #ffffff;
    border: none;
    padding: 12px 20px;
    font-size: 0.95rem;
    font-weight: 600;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: background var(--transition-fast), box-shadow var(--transition-fast);
    box-shadow: 0 4px 12px var(--submit-shadow);
}

.disclaimer-accept:hover {
    background: var(--brand-gradient-hover);
    box-shadow: 0 6px 16px var(--submit-shadow-hover);
}

.disclaimer-accept:focus {
    outline: none;
    box-shadow: var(--focus-ring);
}

.container {
    width: 100%;
    max-width: 500px;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

header {
    text-align: center;
    animation: fadeInDown 0.6s ease-out;
}

.logo-icon {
    display: inline-flex;
    justify-content: center;
    align-items: center;
    width: 64px;
    height: 64px;
    border-radius: 50%;
    background: var(--brand-gradient);
    margin-bottom: var(--spacing-md);
    box-shadow: 0 8px 32px rgba(59, 130, 246, 0.3);
}

.logo-icon svg {
    color: white;
}

h1 {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: var(--spacing-sm);
    letter-spacing: -0.02em;
}

header p {
    color: var(--text-secondary);
    font-size: 1rem;
}

.welcome-card, .calculator-card, .results-card {
    background: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    box-shadow: 0 10px 40px var(--card-shadow);
    animation: fadeInUp 0.6s ease-out 0.1s both;
}

.welcome-card h2 {
    font-size: 1.25rem;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.purpose-text {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
}

.logic-details {
    background: var(--logic-box-bg);
    border-radius: var(--radius-md);
    border: 1px solid var(--details-border);
    overflow: hidden;
}

.logic-details summary {
    padding: 12px 16px;
    cursor: pointer;
    font-weight: 500;
    color: var(--text-accent);
    user-select: none;
    transition: background var(--transition-fast);
}

.logic-details summary:hover {
    background: rgba(255, 255, 255, 0.05);
}

.logic-content {
    padding: 0 16px 16px 16px;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.logic-content p {
    margin-top: 12px;
    margin-bottom: 6px;
}

.logic-content strong {
    color: var(--text-primary);
}

.formula-code {
    display: block;
    background: var(--code-bg);
    padding: 8px 12px;
    border-radius: 6px;
    font-family: var(--font-mono);
    color: var(--code-text);
    border: 1px solid var(--code-border);
    word-break: break-all;
}

fieldset {
    border: none;
    padding: 0;
    margin: 0;
}

.form-group {
    margin-bottom: var(--spacing-lg);
}

.form-group label {
    display: block;
    margin-bottom: var(--spacing-sm);
    font-weight: 500;
    color: var(--text-primary);
    font-size: 0.95rem;
}

.input-group {
    display: flex;
    gap: var(--spacing-sm);
}

input[type="number"], select {
    background-color: var(--input-bg);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    font-family: var(--font-sans);
    font-size: 1rem;
    padding: 12px 16px;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

input[type="number"] {
    flex: 2;
    width: 100%;
}

input[type="number"]::placeholder {
    color: var(--placeholder);
}

select {
    flex: 1;
    cursor: pointer;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%23adb5bd' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 12px center;
    padding-right: 36px;
}

html[data-theme="light"] select {
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%23475569' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
}

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

input:focus, select:focus {
    outline: none;
    border-color: var(--text-accent);
    box-shadow: var(--focus-ring);
    background-color: var(--input-bg-focus);
}

input:hover, select:hover {
    border-color: rgba(255, 255, 255, 0.3);
}

.error-message {
    color: var(--error-color);
    font-size: 0.85rem;
    margin-top: 6px;
    min-height: 20px;
}

.submit-btn {
    width: 100%;
    background: var(--brand-gradient);
    color: white;
    border: none;
    padding: 14px 24px;
    font-size: 1rem;
    font-weight: 600;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: 0 4px 12px rgba(59, 130, 246, 0.2);
}

.submit-btn:hover {
    background: var(--brand-gradient-hover);
    transform: translateY(-2px);
    box-shadow: 0 6px 16px rgba(59, 130, 246, 0.3);
}

.submit-btn:focus {
    outline: none;
    box-shadow: var(--focus-ring);
}

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

/* Results Section */
.results-card {
    padding: var(--spacing-lg) var(--spacing-xl);
    animation: fadeInUp 0.4s ease-out;
}

.results-card.hidden {
    display: none;
}

.results-card h2 {
    font-size: 1.25rem;
    margin-bottom: var(--spacing-lg);
    padding-bottom: var(--spacing-sm);
    border-bottom: 1px solid var(--border-color);
    color: var(--text-primary);
}

.report-grid {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.report-item {
    display: flex;
    flex-direction: column;
}

.report-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: 2px;
}

.report-value {
    font-family: var(--font-mono);
    font-size: 1.1rem;
    color: var(--text-primary);
}

.report-sub {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.report-value.highlight {
    color: var(--text-accent);
    font-weight: 600;
    font-family: var(--font-sans);
}

.primary-result {
    margin: var(--spacing-sm) 0;
    padding: var(--spacing-md);
    background: var(--primary-result-bg);
    border-radius: var(--radius-md);
    border: 1px solid var(--primary-result-border);
}

.snellen-score {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-snellen);
    text-shadow: 0 2px 10px var(--text-snellen-shadow);
}

.divider {
    height: 1px;
    background: var(--border-color);
    margin: var(--spacing-sm) 0;
}

.report-item--conversions {
    margin-top: var(--spacing-md);
}

.report-item--conversions .report-label {
    text-transform: none;
    letter-spacing: 0.02em;
    font-size: 0.8rem;
    font-weight: 600;
}

.report-item--alt {
    margin-left: var(--spacing-sm);
    padding-left: var(--spacing-md);
    border-left: 2px solid var(--border-color);
}

/* Keyframes */
@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 */
@media (max-width: 480px) {
    .calculator-card, .results-card {
        padding: var(--spacing-md);
    }
    .input-group {
        flex-direction: column;
    }
    select {
        width: 100%;
    }
}

/* Footer Styling */
.site-footer {
    text-align: center;
    padding-top: var(--spacing-md);
    padding-bottom: var(--spacing-sm);
    color: var(--text-secondary);
    font-size: 0.85rem;
    animation: fadeInUp 0.6s ease-out 0.2s both;
}