/* Body styles - Sets the overall page background, font, and removes default margins/padding */
/* Reason: Creates a full-screen gradient background for visual appeal and ensures consistent typography across the problems list page */
body {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    padding: 0;
    margin: 0;
}

/* Header section styles - Hero area with title and subtitle */
/* Reason: Provides a prominent header area with white text on the gradient background for page branding and navigation context */
.header-section {
    padding: 40px 0 20px;
    color: white;
    text-align: center;
}

.header-section h1 {
    font-size: 2.5rem;
    font-weight: bold;
    margin-bottom: 15px;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
}

.header-section .subtitle {
    font-size: 1.2rem;
    opacity: 0.95;
}

/* Home button styles - Navigation buttons in header */
/* Reason: Provides accessible navigation back to home page with modern glassmorphism design and hover effects */
.home-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 45px;
    height: 45px;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    color: #667eea;
    text-decoration: none;
    border-radius: 12px;
    font-weight: 600;
    transition: all 0.3s ease;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
    font-size: 18px;
}

.home-btn:hover {
    background: linear-gradient(135deg, #667eea 0%, #3516a6 100%);
    color: #ffffff;
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0,0,0,0.3);
}

/* Content container - Centers and constrains main content width */
/* Reason: Creates a readable content area that doesn't stretch too wide on large screens while maintaining responsive padding */
.content-container {
    max-width: 800px;
    margin: 0 auto 60px;
    padding: 0 20px;
}

/* Card styles - White content boxes with shadow and animation */
/* Reason: Provides clean, elevated content containers that stand out from the background with smooth entrance animation */
.card {
    background: white;
    border-radius: 20px;
    padding: 30px;
    box-shadow: 0 10px 40px rgba(0,0,0,0.2);
    border: none;
    animation: fadeInUp 0.6s ease;
}

.card-title {
    color: #667eea;
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 25px;
    text-align: center;
}

/* List group styles - Container for list items */
/* Reason: Provides consistent spacing between list items */
.list-group {
    gap: 12px;
}

/* List group item styles - Individual list entries with hover effects */
/* Reason: Creates interactive list items with gradient backgrounds and smooth transitions for better user experience */
.list-group-item {
    border: none;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    border-radius: 15px;
    padding: 18px 25px;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.list-group-item:hover {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    transform: translateX(10px);
    box-shadow: 0 6px 20px rgba(102, 126, 234, 0.4);
}

/* List item link styles - Removes default link styling and provides proper layout */
/* Reason: Ensures links within list items are properly styled and don't interfere with the hover effects */
.list-group-item a {
    text-decoration: none;
    color: #333;
    font-weight: 600;
    font-size: 1.05rem;
    flex: 1;
    display: flex;
    align-items: center;
    gap: 12px;
}

.list-group-item:hover a {
    color: white;
}

/* List icon styles - Icons within list items */
/* Reason: Provides consistent sizing and alignment for icons (emoji/file icons) in list items */
.list-icon {
    font-size: 1.2rem;
    min-width: 30px;
    text-align: center;
}

/* List number styles - Number badges on the right side */
/* Reason: Creates numbered badges for list items with theme-consistent colors and hover state changes */
.list-number {
    background: rgba(102, 126, 234, 0.2);
    color: #667eea;
    padding: 5px 12px;
    border-radius: 20px;
    font-weight: 700;
    font-size: 0.9rem;
    min-width: 40px;
    text-align: center;
}

.list-group-item:hover .list-number {
    background: rgba(255, 255, 255, 0.3);
    color: white;
}

/* Animation keyframes for fade in effect */
/* Reason: Provides smooth entrance animation for content cards to enhance perceived performance */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Mobile responsive styles */
/* Reason: Optimizes the layout for mobile devices by reducing font sizes and padding for better touch interaction */
@media (max-width: 768px) {
    .header-section h1 {
        font-size: 2rem;
    }

    .card {
        padding: 20px;
    }

    .list-group-item {
        padding: 15px 20px;
    }

    .list-group-item a {
        font-size: 1rem;
    }
}