/* ==========================================================================
   1. RESET A ZÁKLADNÍ NASTAVENÍ (Box-sizing podle zadání)
   ========================================================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    /* Barevná paleta - Vesmírný temný režim s vysokým kontrastem */
    --bg-space: #0b0d17;
    --bg-card: #151926;
    --text-main: #f0f2f5;
    --text-muted: #b0b5c1;
    --accent-blue: #4f46e5;
    --accent-cyan: #06b6d4;
    --white: #ffffff;
    
    /* Typografie */
    --font-primary: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
}

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: var(--font-primary);
    background-color: var(--bg-space);
    color: var(--text-main);
    line-height: 1.6;
}

/* Pomocný kontejner pro zarovnání obsahu */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Přístupnost: Skrytí prvku pro běžné oči, ale čitelné pro čtečky obrazovky */
.sr-only-skip {
    position: absolute;
    left: -10000px;
    top: auto;
    width: 1px;
    height: 1px;
    overflow: hidden;
}
.sr-only-skip:focus {
    position: static;
    width: auto;
    height: auto;
    background: var(--accent-cyan);
    color: var(--bg-space);
    padding: 10px;
    display: block;
    text-align: center;
    font-weight: bold;
}

/* Klávesnicový focus pro lepší přístupnost (WCAG) */
a:focus, button:focus, input:focus {
    outline: 3px solid var(--accent-cyan);
    outline-offset: 2px;
}

/* ==========================================================================
   2. HLAVIČKA A NAVIGACE (Flexbox)
   ========================================================================== */
.main-header {
    background-color: rgba(21, 25, 38, 0.9);
    backdrop-filter: blur(10px);
    position: sticky;
    top: 0;
    z-index: 100;
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.header-wrapper {
    display: flex;
    flex-direction: column; /* Mobile first: pod sebou */
    align-items: center;
    padding: 15px 20px;
}

.logo a {
    font-size: 1.4rem;
    font-weight: bold;
    color: var(--white);
    text-decoration: none;
}

.main-nav {
    margin-top: 15px;
}

.main-nav ul {
    display: flex;
    list-style: none;
    gap: 20px;
}

.main-nav a {
    color: var(--text-muted);
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s ease;
    padding: 5px 10px;
}

.main-nav a:hover, .main-nav a.active {
    color: var(--accent-cyan);
}

/* ==========================================================================
   3. HERO SEKCE (Úvodní banner)
   ========================================================================== */
.hero-section {
    padding: 80px 0;
    text-align: center;
    background: radial-gradient(circle at center, #1e1b4b 0%, var(--bg-space) 70%);
}

.hero-content h1 {
    font-size: 2.5rem;
    color: var(--white);
    margin-bottom: 20px;
    line-height: 1.2;
}

.hero-content p {
    font-size: 1.1rem;
    color: var(--text-muted);
    max-width: 600px;
    margin: 0 auto 30px auto;
}

/* Tlačítka */
.btn {
    display: inline-block;
    padding: 12px 28px;
    border-radius: 8px;
    font-weight: 600;
    text-decoration: none;
    cursor: pointer;
    transition: background-color 0.3s ease, transform 0.2s ease;
    border: none;
}

.btn-primary {
    background-color: var(--accent-blue);
    color: var(--white);
}

.btn-primary:hover {
    background-color: #4338ca;
    transform: translateY(-2px);
}

.btn-secondary {
    background-color: transparent;
    border: 2px solid var(--accent-cyan);
    color: var(--accent-cyan);
    width: 100%;
}

.btn-secondary:hover {
    background-color: var(--accent-cyan);
    color: var(--bg-space);
}

/* ==========================================================================
   4. ENCYKLOPEDIE PLANET (CSS Grid - Mobile First)
   ========================================================================== */
.planets-section {
    padding: 60px 0;
}

.planets-section h2, .calculator-section h2 {
    font-size: 2rem;
    text-align: center;
    color: var(--white);
    margin-bottom: 10px;
}

.section-subtitle {
    text-align: center;
    color: var(--text-muted);
    margin-bottom: 40px;
}

/* CSS Grid definice pro karty */
.planets-grid {
    display: grid;
    grid-template-columns: 1fr; /* Na mobilu 1 sloupec */
    gap: 30px;
}

.planet-card {
    background-color: var(--bg-card);
    border-radius: 12px;
    overflow: hidden;
    border: 1px solid rgba(255, 255, 255, 0.05);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.planet-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 20px rgba(6, 182, 212, 0.1);
}

.planet-card img {
    width: 100%;
    height: 250px;
    object-fit: cover; /* Aby se obrázek nedeformoval */
    background-color: #000; /* fallback než se načte obrázek */
}

.card-body {
    padding: 25px;
}

.card-body h3 {
    font-size: 1.5rem;
    color: var(--white);
    margin-bottom: 10px;
}

.card-body p {
    color: var(--text-muted);
    margin-bottom: 20px;
    font-size: 0.95rem;
}

/* ==========================================================================
   5. KALKULAČKA (Flexbox / Form styling)
   ========================================================================== */
.calculator-section {
    padding: 60px 0;
    background-color: rgba(21, 25, 38, 0.5);
}

.calculator-wrapper {
    max-width: 600px;
    margin: 0 auto;
}

.calc-form {
    margin-top: 30px;
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.form-group label {
    font-weight: 500;
    color: var(--text-main);
}

.form-group input {
    padding: 12px;
    border-radius: 8px;
    border: 2px solid rgba(255, 255, 255, 0.1);
    background-color: var(--bg-space);
    color: var(--white);
    font-size: 1rem;
}

.calc-result {
    margin-top: 30px;
    padding: 20px;
    border-radius: 8px;
    background-color: var(--bg-card);
    border-left: 4px solid var(--accent-cyan);
    min-height: 50px;
}

/* ==========================================================================
   6. PATIČKA
   ========================================================================== */
.main-footer {
    padding: 40px 0;
    border-top: 1px solid rgba(255, 255, 255, 0.05);
    text-align: center;
    color: var(--text-muted);
    font-size: 0.9rem;
}

.footer-wrapper p + p {
    margin-top: 5px;
}

/* ==========================================================================
   7. RESPONSIVE DESIGN (Média dotazy pro Tablet a Desktop)
   ========================================================================== */

/* Tablet a širší (nad 600px) */
@media (min-width: 600px) {
    .header-wrapper {
        flex-direction: row; /* Navigace a logo vedle sebe */
        justify-content: space-between;
    }
    
    .main-nav {
        margin-top: 0;
    }
    
    .planets-grid {
        grid-template-columns: repeat(2, 1fr); /* 2 karty vedle sebe */
    }
    
    .hero-content h1 {
        font-size: 3.5rem;
    }
}

/* Velký desktop (nad 900px) */
@media (min-width: 900px) {
    .planets-grid {
        grid-template-columns: repeat(3, 1fr); /* 3 karty vedle sebe */
    }
}