/* ============================================
   DESIGN SYSTEM — Engineer's Portfolio
   Inspired by GitHub, Cloudflare, Stripe Docs
   ============================================ */

/* Light mode */
:root {
    --bg-color: #FFFFFF;
    --text-color: #111827;
    --text-secondary: #6B7280;
    --text-muted: #9CA3AF;
    --border-color: #E5E7EB;
    --card-bg: #FFFFFF;
    --card-border: #E5E7EB;
    --card-hover-shadow: rgba(0, 0, 0, 0.06);
    --tag-bg: #F3F4F6;
    --tag-text: #374151;
    --accent: #2563EB;
    --accent-subtle: #EFF6FF;
    --input-bg: #FFFFFF;
    --section-alt-bg: #F9FAFB;
    --detail-bg: #F9FAFB;
    --link-hover: #111827;
}

/* Dark mode */
[data-theme="dark"] {
    --bg-color: #0D1117;
    --text-color: #F3F4F6;
    --text-secondary: #9CA3AF;
    --text-muted: #6B7280;
    --border-color: #30363D;
    --card-bg: #161B22;
    --card-border: #30363D;
    --card-hover-shadow: rgba(0, 0, 0, 0.3);
    --tag-bg: #21262D;
    --tag-text: #C9D1D9;
    --accent: #58A6FF;
    --accent-subtle: #161B22;
    --input-bg: #0D1117;
    --section-alt-bg: #161B22;
    --detail-bg: #161B22;
    --link-hover: #F3F4F6;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background: var(--bg-color);
    transition: background-color 0.3s ease, color 0.3s ease;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

html {
    scroll-behavior: smooth;
}

.container {
    max-width: 960px;
    margin: 0 auto;
    padding: 0 24px;
}

/* ============================================
   HEADER / HERO
   ============================================ */

header {
    padding: 80px 0 64px;
    border-bottom: 1px solid var(--border-color);
    position: relative;
}

.hero-content {
    max-width: 640px;
}

h1 {
    font-size: 2rem;
    font-weight: 600;
    letter-spacing: -0.025em;
    line-height: 1.2;
    margin-bottom: 8px;
}

.hero-title {
    font-size: 1.125rem;
    color: var(--text-secondary);
    font-weight: 500;
    margin-bottom: 20px;
}

.hero-description {
    font-size: 1.0625rem;
    color: var(--text-secondary);
    line-height: 1.7;
    margin-bottom: 32px;
    max-width: 560px;
}

.hero-actions {
    display: flex;
    align-items: center;
    gap: 12px;
    flex-wrap: wrap;
}

.btn {
    display: inline-flex;
    align-items: center;
    padding: 8px 20px;
    border-radius: 6px;
    font-size: 0.875rem;
    font-weight: 500;
    text-decoration: none;
    transition: all 0.15s ease;
    cursor: pointer;
    border: 1px solid transparent;
}

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

.btn-primary:hover {
    opacity: 0.85;
    transform: translateY(-1px);
}

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

.btn-secondary:hover {
    background: var(--tag-bg);
    transform: translateY(-1px);
}

.btn-link {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.875rem;
    font-weight: 500;
    padding: 8px 12px;
    border-radius: 6px;
    transition: all 0.15s ease;
}

.btn-link:hover {
    color: var(--text-color);
    background: var(--tag-bg);
}

.btn-link svg {
    opacity: 0.7;
}

/* ============================================
   THEME TOGGLE
   ============================================ */

.theme-toggle {
    position: absolute;
    top: 20px;
    right: 0;
}

#themeToggle {
    background: transparent;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    width: 36px;
    height: 36px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.15s ease;
    color: var(--text-color);
}

#themeToggle:hover {
    background: var(--tag-bg);
}

.sun-icon {
    display: block;
}

.moon-icon {
    display: none;
}

[data-theme="dark"] .sun-icon {
    display: none;
}

[data-theme="dark"] .moon-icon {
    display: block;
}

/* ============================================
   SECTIONS — General
   ============================================ */

section {
    padding: 64px 0;
    border-bottom: 1px solid var(--border-color);
}

section:last-of-type {
    border-bottom: none;
}

h2 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 32px;
    letter-spacing: -0.01em;
    color: var(--text-color);
}

/* ============================================
   WHAT I BUILD
   ============================================ */

.build-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 16px;
}

.build-card {
    padding: 24px;
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: 8px;
    transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.build-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px var(--card-hover-shadow);
}

.build-card-icon {
    color: var(--text-muted);
    margin-bottom: 12px;
}

.build-card h3 {
    font-size: 0.9375rem;
    font-weight: 600;
    margin-bottom: 8px;
    color: var(--text-color);
}

.build-card p {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ============================================
   IMPACT
   ============================================ */

.impact-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 16px;
}

.impact-card {
    text-align: center;
    padding: 24px 16px;
    border: 1px solid var(--card-border);
    border-radius: 8px;
    background: var(--card-bg);
}

.impact-number {
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--text-color);
    letter-spacing: -0.025em;
    margin-bottom: 4px;
}

.impact-label {
    font-size: 0.8125rem;
    color: var(--text-secondary);
}

/* ============================================
   PROJECT FILTERS
   ============================================ */

.project-filters {
    display: flex;
    gap: 8px;
    margin-bottom: 24px;
    flex-wrap: wrap;
}

.filter-btn {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    padding: 6px 16px;
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.8125rem;
    font-weight: 500;
    transition: all 0.15s ease;
    font-family: inherit;
}

.filter-btn:hover {
    color: var(--text-color);
    border-color: var(--text-muted);
}

.filter-btn.active {
    background: var(--text-color);
    color: var(--bg-color);
    border-color: var(--text-color);
}

/* ============================================
   PROJECTS GRID (Homepage)
   ============================================ */

.projects-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 16px;
}

.project-card {
    display: flex;
    flex-direction: column;
    padding: 24px;
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: 8px;
    text-decoration: none;
    color: inherit;
    transition: transform 0.15s ease, box-shadow 0.15s ease;
    cursor: pointer;
}

.project-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px var(--card-hover-shadow);
}

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

.project-card-header {
    display: flex;
    align-items: flex-start;
    gap: 8px;
    margin-bottom: 12px;
}

.project-card-header svg {
    flex-shrink: 0;
    color: var(--text-muted);
    margin-top: 2px;
}

.project-card-header h3 {
    font-size: 0.9375rem;
    font-weight: 600;
    color: var(--text-color);
    line-height: 1.3;
}

.project-card > p {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 12px;
    flex: 1;
}

.project-impact-line {
    font-size: 0.8125rem;
    color: var(--text-muted);
    padding: 8px 12px;
    background: var(--detail-bg);
    border-radius: 4px;
    margin-bottom: 12px;
    border-left: 2px solid var(--border-color);
    line-height: 1.5;
}

/* Tech tags */
.tech-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    margin-top: auto;
}

.tech-tag {
    background: var(--tag-bg);
    color: var(--tag-text);
    padding: 3px 10px;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 500;
}

.projects-cta {
    text-align: center;
    margin-top: 32px;
}

/* ============================================
   EXPERIENCE
   ============================================ */

.experience-list {
    display: flex;
    flex-direction: column;
    gap: 0;
}

.experience-item {
    padding: 24px 0;
    border-bottom: 1px solid var(--border-color);
}

.experience-item:first-child {
    padding-top: 0;
}

.experience-item:last-child {
    border-bottom: none;
    padding-bottom: 0;
}

.experience-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 16px;
    margin-bottom: 8px;
}

.experience-header h3 {
    font-size: 0.9375rem;
    font-weight: 600;
    color: var(--text-color);
}

.experience-company {
    font-size: 0.875rem;
    color: var(--text-secondary);
    margin-top: 2px;
}

.experience-period {
    font-size: 0.8125rem;
    color: var(--text-muted);
    white-space: nowrap;
    flex-shrink: 0;
}

.experience-description {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ============================================
   TECHNOLOGY STACK
   ============================================ */

.stack-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 24px;
}

.stack-category h3 {
    font-size: 0.8125rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 12px;
}

.stack-items {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.stack-item {
    padding: 6px 14px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 0.8125rem;
    font-weight: 500;
    color: var(--text-color);
    background: var(--card-bg);
}

/* ============================================
   CONTACT
   ============================================ */

.contact-content {
    max-width: 560px;
}

.contact-content > p {
    font-size: 1rem;
    color: var(--text-secondary);
    line-height: 1.7;
    margin-bottom: 32px;
}

.contact-form {
    margin-bottom: 40px;
    background: var(--card-bg);
    padding: 24px;
    border-radius: 8px;
    border: 1px solid var(--border-color);
}

.contact-form .form-group {
    margin-bottom: 20px;
    text-align: left;
}

.contact-form label {
    display: block;
    margin-bottom: 6px;
    font-weight: 500;
    color: var(--text-color);
    font-size: 0.875rem;
}

.contact-form input,
.contact-form textarea {
    width: 100%;
    padding: 10px 14px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 0.9375rem;
    background: var(--input-bg);
    color: var(--text-color);
    transition: border-color 0.15s ease, box-shadow 0.15s ease;
    font-family: inherit;
}

.contact-form input:focus,
.contact-form textarea:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.contact-form textarea {
    resize: vertical;
    min-height: 120px;
}

.contact-form button {
    display: inline-block;
    background: var(--text-color);
    color: var(--bg-color);
    padding: 10px 24px;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.875rem;
    font-weight: 600;
    font-family: inherit;
    transition: opacity 0.15s ease, transform 0.15s ease;
}

.contact-form button:hover {
    opacity: 0.85;
    transform: translateY(-1px);
}

.contact-form button:active {
    transform: translateY(0);
}

.contact-form button:disabled {
    background: var(--text-muted);
    cursor: not-allowed;
}

.form-status {
    margin-top: 16px;
    padding: 10px 14px;
    border-radius: 6px;
    font-size: 0.875rem;
    display: none;
    text-align: center;
}

.form-status.success {
    display: block;
    background: #ECFDF5;
    color: #065F46;
    border: 1px solid #A7F3D0;
}

[data-theme="dark"] .form-status.success {
    background: #064E3B;
    color: #A7F3D0;
    border-color: #065F46;
}

.form-status.error {
    display: block;
    background: #FEF2F2;
    color: #991B1B;
    border: 1px solid #FECACA;
}

[data-theme="dark"] .form-status.error {
    background: #450A0A;
    color: #FECACA;
    border-color: #991B1B;
}

.form-status.loading {
    display: block;
    background: var(--tag-bg);
    color: var(--text-secondary);
    border: 1px solid var(--border-color);
}

.form-status.info {
    display: block;
    background: var(--tag-bg);
    color: var(--text-secondary);
    border: 1px solid var(--border-color);
    margin-top: 16px;
    padding: 10px 14px;
    border-radius: 6px;
    text-align: center;
}

.turnstile-wrapper {
    margin: 20px 0;
    display: flex;
    justify-content: center;
}

.contact-info {
    display: flex;
    gap: 40px;
    flex-wrap: wrap;
    padding-top: 24px;
    border-top: 1px solid var(--border-color);
}

.contact-item {
    text-align: left;
}

.contact-item strong {
    display: block;
    margin-bottom: 4px;
    color: var(--text-color);
    font-size: 0.8125rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.contact-item span {
    color: var(--text-secondary);
    font-size: 0.9375rem;
}

/* ============================================
   FOOTER
   ============================================ */

footer {
    padding: 32px 0;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.8125rem;
}

/* ============================================
   BACK TO TOP
   ============================================ */

.back-to-top {
    position: fixed;
    bottom: 24px;
    right: 24px;
    width: 40px;
    height: 40px;
    background: var(--card-bg);
    color: var(--text-color);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transition: all 0.15s ease;
    z-index: 1000;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}

.back-to-top:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px var(--card-hover-shadow);
}

/* ============================================
   ANIMATIONS
   ============================================ */

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(8px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ============================================
   RESPONSIVE
   ============================================ */

@media (max-width: 768px) {
    header {
        padding: 60px 0 48px;
    }

    h1 {
        font-size: 1.75rem;
    }

    .hero-description {
        font-size: 1rem;
    }

    .hero-actions {
        gap: 8px;
    }

    section {
        padding: 48px 0;
    }

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

    .impact-grid {
        grid-template-columns: repeat(2, 1fr);
    }

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

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

    .experience-header {
        flex-direction: column;
        gap: 4px;
    }

    .contact-info {
        flex-direction: column;
        gap: 16px;
    }

    .theme-toggle {
        top: 16px;
    }

    .project-filters {
        gap: 6px;
    }

    .filter-btn {
        padding: 5px 12px;
        font-size: 0.75rem;
    }

    .back-to-top {
        bottom: 16px;
        right: 16px;
        width: 36px;
        height: 36px;
    }
}

@media (max-width: 480px) {
    .impact-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 8px;
    }

    .impact-card {
        padding: 16px 8px;
    }

    .impact-number {
        font-size: 1.375rem;
    }
}

/* ============================================
   ACCESSIBILITY
   ============================================ */

.skip-to-content {
    position: absolute;
    left: -9999px;
    z-index: 999;
}

.skip-to-content:focus {
    left: 50%;
    transform: translateX(-50%);
    top: 10px;
}