/* ===================================
   CSS Variables - Light & Dark Themes
   =================================== */

:root {
    /* Light Theme (Default) */
    --color-bg-primary: #ffffff;
    --color-bg-secondary: #f8fafc;
    --color-bg-tertiary: #f1f5f9;
    --color-bg-elevated: #ffffff;
    --color-bg-overlay: rgba(0, 0, 0, 0.5);

    --color-text-primary: #0f172a;
    --color-text-secondary: #475569;
    --color-text-tertiary: #94a3b8;
    --color-text-inverse: #ffffff;

    --color-primary: #6366f1;
    --color-primary-hover: #4f46e5;
    --color-primary-active: #4338ca;
    --color-primary-light: #eef2ff;
    --color-primary-lighter: #e0e7ff;

    --color-secondary: #8b5cf6;
    --color-secondary-hover: #7c3aed;
    --color-secondary-light: #f3e8ff;

    --color-accent: #06b6d4;
    --color-accent-hover: #0891b2;
    --color-accent-light: #cffafe;

    --color-success: #10b981;
    --color-success-light: #d1fae5;
    --color-warning: #f59e0b;
    --color-warning-light: #fef3c7;
    --color-error: #ef4444;
    --color-error-light: #fee2e2;
    --color-info: #3b82f6;
    --color-info-light: #dbeafe;

    --color-border: #e2e8f0;
    --color-border-light: #f1f5f9;
    --color-border-focus: #6366f1;

    --color-shadow-sm: rgba(0, 0, 0, 0.05);
    --color-shadow-md: rgba(0, 0, 0, 0.1);
    --color-shadow-lg: rgba(0, 0, 0, 0.15);
    --color-shadow-xl: rgba(0, 0, 0, 0.2);

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    --spacing-3xl: 4rem;
    --spacing-4xl: 6rem;

    /* Typography */
    --font-family-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-family-mono: ui-monospace, SFMono-Regular, 'SF Mono', Menlo, Consolas, 'Liberation Mono', monospace;

    --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;
    --font-size-5xl: 3rem;
    --font-size-6xl: 3.75rem;

    --font-weight-normal: 400;
    --font-weight-medium: 500;
    --font-weight-semibold: 600;
    --font-weight-bold: 700;

    --line-height-tight: 1.25;
    --line-height-snug: 1.375;
    --line-height-normal: 1.5;
    --line-height-relaxed: 1.625;
    --line-height-loose: 2;

    --letter-spacing-tight: -0.025em;
    --letter-spacing-normal: 0;
    --letter-spacing-wide: 0.025em;

    /* Layout */
    --container-max-width: 1200px;
    --container-padding: var(--spacing-lg);
    --border-radius-sm: 0.25rem;
    --border-radius-md: 0.5rem;
    --border-radius-lg: 0.75rem;
    --border-radius-xl: 1rem;
    --border-radius-full: 9999px;

    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-normal: 250ms ease-in-out;
    --transition-slow: 350ms ease-in-out;

    /* Shadows */
    --shadow-sm: 0 1px 2px 0 var(--color-shadow-sm);
    --shadow-md: 0 4px 6px -1px var(--color-shadow-md), 0 2px 4px -1px var(--color-shadow-md);
    --shadow-lg: 0 10px 15px -3px var(--color-shadow-lg), 0 4px 6px -2px var(--color-shadow-lg);
    --shadow-xl: 0 20px 25px -5px var(--color-shadow-xl), 0 10px 10px -5px var(--color-shadow-xl);
    --shadow-focus: 0 0 0 3px var(--color-primary-light);

    /* Z-index */
    --z-index-base: 1;
    --z-index-dropdown: 100;
    --z-index-sticky: 200;
    --z-index-fixed: 300;
    --z-index-modal-backdrop: 400;
    --z-index-modal: 500;
    --z-index-popover: 600;
    --z-index-tooltip: 700;
}

/* Dark Theme */
[data-theme="dark"] {
    --color-bg-primary: #0f172a;
    --color-bg-secondary: #1e293b;
    --color-bg-tertiary: #334155;
    --color-bg-elevated: #1e293b;
    --color-bg-overlay: rgba(0, 0, 0, 0.7);

    --color-text-primary: #f8fafc;
    --color-text-secondary: #cbd5e1;
    --color-text-tertiary: #64748b;
    --color-text-inverse: #0f172a;

    --color-primary: #818cf8;
    --color-primary-hover: #6366f1;
    --color-primary-active: #4f46e5;
    --color-primary-light: rgba(129, 140, 248, 0.15);
    --color-primary-lighter: rgba(129, 140, 248, 0.25);

    --color-secondary: #a78bfa;
    --color-secondary-hover: #8b5cf6;
    --color-secondary-light: rgba(167, 139, 250, 0.15);

    --color-accent: #22d3ee;
    --color-accent-hover: #06b6d4;
    --color-accent-light: rgba(34, 211, 238, 0.15);

    --color-success: #34d399;
    --color-success-light: rgba(52, 211, 153, 0.15);
    --color-warning: #fbbf24;
    --color-warning-light: rgba(251, 191, 36, 0.15);
    --color-error: #f87171;
    --color-error-light: rgba(248, 113, 113, 0.15);
    --color-info: #60a5fa;
    --color-info-light: rgba(96, 165, 250, 0.15);

    --color-border: #334155;
    --color-border-light: #1e293b;
    --color-border-focus: #818cf8;

    --color-shadow-sm: rgba(0, 0, 0, 0.3);
    --color-shadow-md: rgba(0, 0, 0, 0.4);
    --color-shadow-lg: rgba(0, 0, 0, 0.5);
    --color-shadow-xl: rgba(0, 0, 0, 0.6);
}

/* ===================================
   CSS Reset & Base Styles
   =================================== */

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

html {
    font-size: 16px;
    scroll-behavior: smooth;
    -webkit-text-size-adjust: 100%;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: var(--font-family-sans);
    font-size: var(--font-size-base);
    font-weight: var(--font-weight-normal);
    line-height: var(--line-height-normal);
    color: var(--color-text-primary);
    background-color: var(--color-bg-primary);
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    transition: background-color var(--transition-normal), color var(--transition-normal);
}

/* Smooth theme transitions for all themeable elements */
body,
.site-header,
.site-footer,
.hero,
.theme-toggle,
.email-input,
.submit-button,
.social-link,
.signup-form {
    transition-property: background-color, color, border-color, box-shadow;
    transition-duration: var(--transition-normal);
    transition-timing-function: ease-in-out;
}

/* Enhanced transitions during theme switching */
body.theme-transitioning,
body.theme-transitioning *,
body.theme-transitioning *::before,
body.theme-transitioning *::after {
    transition-property: background-color, color, border-color, box-shadow, transform !important;
    transition-duration: 300ms !important;
    transition-timing-function: ease-in-out !important;
}

/* Focus styles for accessibility */
:focus-visible {
    outline: 2px solid var(--color-border-focus);
    outline-offset: 2px;
}

:focus:not(:focus-visible) {
    outline: none;
}

/* Ensure focus states are visible for all interactive elements */
button:focus-visible,
a:focus-visible,
input:focus-visible {
    outline: 2px solid var(--color-border-focus);
    outline-offset: 2px;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: var(--font-weight-bold);
    line-height: var(--line-height-tight);
    margin-bottom: var(--spacing-md);
    color: var(--color-text-primary);
}

h1 { font-size: var(--font-size-5xl); }
h2 { font-size: var(--font-size-4xl); }
h3 { font-size: var(--font-size-3xl); }
h4 { font-size: var(--font-size-2xl); }
h5 { font-size: var(--font-size-xl); }
h6 { font-size: var(--font-size-lg); }

p {
    margin-bottom: var(--spacing-md);
}

a {
    color: var(--color-primary);
    text-decoration: none;
    transition: color var(--transition-fast);
}

a:hover {
    color: var(--color-primary-hover);
}

/* Lists */
ul, ol {
    list-style: none;
}

/* Images */
img {
    max-width: 100%;
    height: auto;
    display: block;
}

/* Buttons */
button {
    font: inherit;
    color: inherit;
    background: none;
    border: none;
    cursor: pointer;
}

/* Forms */
input, textarea, select, button {
    font: inherit;
    color: inherit;
}

/* ===================================
   Utility Classes
   =================================== */

.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

.skip-link {
    position: absolute;
    top: -100%;
    left: 0;
    background: var(--color-primary);
    color: var(--color-text-inverse);
    padding: var(--spacing-sm) var(--spacing-md);
    z-index: var(--z-index-tooltip);
    transition: top var(--transition-fast);
}

.skip-link:focus {
    top: 0;
}

.container {
    width: 100%;
    max-width: var(--container-max-width);
    margin: 0 auto;
    padding: 0 var(--container-padding);
}

/* ===================================
   Header Styles
   =================================== */

.site-header {
    position: sticky;
    top: 0;
    z-index: var(--z-index-sticky);
    background: var(--color-bg-elevated);
    border-bottom: 1px solid var(--color-border);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    transition: background-color var(--transition-normal), border-color var(--transition-normal);
}

.header-content {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md) 0;
}

.logo {
    width: auto;
    height: 40px;
    max-width: 100%;
}

/* Responsive header adjustments */
@media (max-width: 575.98px) {
    .logo {
        height: 32px;
    }

    .header-content {
        padding: var(--spacing-sm) 0;
    }
}

.theme-toggle {
    position: relative;
    width: 44px;
    height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--color-bg-secondary);
    border: 2px solid transparent;
    border-radius: var(--border-radius-full);
    cursor: pointer;
    transition: background-color var(--transition-fast), border-color var(--transition-fast), transform var(--transition-fast);
}

.theme-toggle:hover {
    background: var(--color-bg-tertiary);
    border-color: var(--color-primary);
    transform: scale(1.05);
}

.theme-toggle:active {
    transform: scale(0.95);
}

.theme-toggle:focus-visible {
    outline: 2px solid var(--color-border-focus);
    outline-offset: 2px;
    box-shadow: var(--shadow-focus);
}

.theme-icon {
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--color-text-primary);
    transition: color var(--transition-fast);
}

.theme-icon svg {
    width: 20px;
    height: 20px;
}

/* Ensure theme toggle is visible on all backgrounds */
.site-header .theme-toggle {
    background: var(--color-bg-secondary);
}

[data-theme="dark"] .site-header .theme-toggle {
    background: var(--color-bg-tertiary);
}

/* ===================================
   Main Content Styles
   =================================== */

.main-content {
    min-height: calc(100vh - 200px);
}

.hero {
    min-height: calc(100vh - 160px);
    display: flex;
    align-items: center;
    padding: var(--spacing-3xl) 0;
    background: linear-gradient(135deg, var(--color-bg-secondary) 0%, var(--color-bg-primary) 100%);
    transition: background var(--transition-normal);
}

.hero-content {
    max-width: 800px;
    margin: 0 auto;
    text-align: center;
}

.hero-title {
    font-size: var(--font-size-5xl);
    font-weight: var(--font-weight-bold);
    letter-spacing: var(--letter-spacing-tight);
    margin-bottom: var(--spacing-lg);
    color: var(--color-text-primary);
}

.hero-title-accent {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hero-description {
    font-size: var(--font-size-xl);
    line-height: var(--line-height-relaxed);
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-2xl);
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

/* ===================================
   Form Styles
   =================================== */

.signup-form {
    max-width: 500px;
    margin: 0 auto var(--spacing-2xl);
}

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

.email-input {
    flex: 1;
    padding: var(--spacing-md) var(--spacing-lg);
    font-size: var(--font-size-base);
    border: 2px solid var(--color-border);
    border-radius: var(--border-radius-lg);
    background: var(--color-bg-elevated);
    color: var(--color-text-primary);
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
    min-height: 44px; /* Touch target size */
}

/* Ensure proper font size on mobile to prevent zoom */
@media (max-width: 767.98px) {
    .email-input {
        font-size: 16px; /* Prevents iOS auto-zoom */
    }
}

.email-input:hover {
    border-color: var(--color-text-tertiary);
}

.email-input:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: var(--shadow-focus);
}

.email-input::placeholder {
    color: var(--color-text-tertiary);
}

.submit-button {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-xl);
    font-size: var(--font-size-base);
    font-weight: var(--font-weight-semibold);
    color: var(--color-text-inverse);
    background: var(--color-primary);
    border: none;
    border-radius: var(--border-radius-lg);
    cursor: pointer;
    transition: background-color var(--transition-fast), transform var(--transition-fast);
}

.submit-button:hover {
    background: var(--color-primary-hover);
    transform: translateY(-1px);
}

.submit-button:active {
    background: var(--color-primary-active);
    transform: translateY(0);
}

.submit-button:focus-visible {
    box-shadow: var(--shadow-focus);
}

.form-help {
    font-size: var(--font-size-sm);
    color: var(--color-text-tertiary);
    margin-top: var(--spacing-sm);
}

.form-message {
    margin-top: var(--spacing-md);
    padding: var(--spacing-md);
    border-radius: var(--border-radius-md);
    font-size: var(--font-size-sm);
    display: none;
}

.form-message.success {
    display: block;
    background: var(--color-success-light);
    color: var(--color-success);
}

.form-message.error {
    display: block;
    background: var(--color-error-light);
    color: var(--color-error);
}

/* ===================================
   Social Links Styles
   =================================== */

.social-links {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
}

.social-link {
    width: 48px;
    height: 48px;
    min-width: 44px; /* Touch target minimum */
    min-height: 44px; /* Touch target minimum */
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--color-text-secondary);
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius-lg);
    transition: color var(--transition-fast), background-color var(--transition-fast), border-color var(--transition-fast), transform var(--transition-fast);
}

.social-link:hover {
    color: var(--color-primary);
    background: var(--color-primary-light);
    border-color: var(--color-primary);
    transform: translateY(-2px);
}

.social-link:active {
    transform: translateY(0);
}

.social-link:focus-visible {
    box-shadow: var(--shadow-focus);
    outline: 2px solid var(--color-border-focus);
    outline-offset: 2px;
}

/* ===================================
   Footer Styles
   =================================== */

.site-footer {
    padding: var(--spacing-xl) 0;
    background: var(--color-bg-secondary);
    border-top: 1px solid var(--color-border);
    transition: background-color var(--transition-normal), border-color var(--transition-normal);
}

.copyright {
    text-align: center;
    font-size: var(--font-size-sm);
    color: var(--color-text-tertiary);
}

/* ===================================
   Responsive Breakpoints
   =================================== */

/* Mobile First Approach */

/* Extra small devices (small phones, 375px and up) */
@media (min-width: 375px) {
    :root {
        --container-padding: var(--spacing-lg);
    }

    .hero-title {
        font-size: var(--font-size-4xl);
    }

    .hero-description {
        font-size: var(--font-size-base);
    }
}

/* Small devices (landscape phones, 576px and up) */
@media (min-width: 576px) {
    :root {
        --container-padding: var(--spacing-xl);
    }

    .hero-title {
        font-size: var(--font-size-5xl);
    }

    .hero-description {
        font-size: var(--font-size-lg);
    }

    .signup-form {
        max-width: 480px;
    }
}

/* Medium devices (tablets, 768px and up) */
@media (min-width: 768px) {
    .form-group {
        flex-direction: row;
        gap: var(--spacing-md);
    }

    .email-input {
        padding: var(--spacing-lg) var(--spacing-xl);
        font-size: var(--font-size-base);
        flex: 1;
    }

    .submit-button {
        padding: var(--spacing-lg) var(--spacing-2xl);
        font-size: var(--font-size-base);
        width: auto;
        min-width: 160px;
    }

    .hero {
        min-height: calc(100vh - 180px);
        padding: var(--spacing-4xl) 0;
    }

    .hero-title {
        font-size: var(--font-size-6xl);
        margin-bottom: var(--spacing-xl);
    }

    .hero-description {
        font-size: var(--font-size-xl);
    }
}

/* Large devices (desktops, 992px and up) */
@media (min-width: 992px) {
    :root {
        --container-max-width: 960px;
    }

    .hero-description {
        font-size: var(--font-size-2xl);
        max-width: 650px;
    }

    .social-links {
        gap: var(--spacing-lg);
    }
}

/* Extra large devices (large desktops, 1200px and up) */
@media (min-width: 1200px) {
    :root {
        --container-max-width: 1140px;
    }

    .social-link {
        width: 56px;
        height: 56px;
    }

    .hero-title {
        font-size: 4rem;
    }

    .hero-description {
        font-size: var(--font-size-2xl);
    }
}

/* Extra extra large devices (4K displays, 1440px and up) */
@media (min-width: 1440px) {
    :root {
        --container-max-width: 1320px;
    }

    .hero-title {
        font-size: 4.5rem;
    }

    .hero-description {
        font-size: var(--font-size-3xl);
    }

    .signup-form {
        max-width: 540px;
    }
}

/* Ultra wide displays (1920px and up) */
@media (min-width: 1920px) {
    :root {
        --container-max-width: 1400px;
        --font-size-base: 1.125rem;
    }

    .hero-title {
        font-size: 5rem;
    }

    .hero-description {
        font-size: var(--font-size-3xl);
    }

    .social-link {
        width: 64px;
        height: 64px;
    }
}

/* Small devices (portrait phones, less than 576px) */
@media (max-width: 575.98px) {
    .form-group {
        flex-direction: column;
    }

    .submit-button {
        width: 100%;
        justify-content: center;
        min-height: 48px;
    }

    .hero-title {
        font-size: var(--font-size-3xl);
    }

    .hero-description {
        font-size: var(--font-size-base);
    }

    .social-link {
        width: 44px;
        height: 44px;
    }

    .site-header {
        padding: var(--spacing-sm) 0;
    }

    .header-content {
        padding: var(--spacing-sm) 0;
    }
}

/* Ensure touch targets meet minimum size (44x44px) */
@media (max-width: 767.98px) {
    .theme-toggle {
        min-width: 44px;
        min-height: 44px;
    }

    .social-link {
        min-width: 44px;
        min-height: 44px;
    }

    .submit-button {
        min-height: 44px;
    }
}

/* Touch device optimizations */
@media (hover: none) and (pointer: coarse) {
    .submit-button,
    .social-link,
    .theme-toggle {
        transition: background-color var(--transition-normal), color var(--transition-normal);
    }

    .submit-button:hover,
    .social-link:hover {
        transform: none;
    }
}

/* Reduced motion preference */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }

    /* Disable hover effects for users who prefer reduced motion */
    .submit-button:hover,
    .social-link:hover,
    .theme-toggle:hover {
        transform: none !important;
    }
}

/* High contrast mode support */
@media (prefers-contrast: high) {
    :root {
        --color-border: #000000;
        --color-border-focus: #6366f1;
    }

    [data-theme="dark"] {
        --color-border: #ffffff;
    }

    .email-input {
        border-width: 3px;
    }
}