/* Reset and base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

/* CSS Custom Properties for consistent spacing */
:root {
    /* Spacing system */
    --space-xs: 0.5rem;   /* 8px */
    --space-sm: 1rem;     /* 16px */
    --space-md: 1.5rem;   /* 24px */
    --space-lg: 2rem;     /* 32px */
    --space-xl: 3rem;     /* 48px */
    --space-2xl: 4rem;    /* 64px */
    
    /* Typography scale */
    --text-xs: 0.75rem;   /* 12px */
    --text-sm: 0.875rem;  /* 14px */
    --text-base: 1rem;    /* 16px */
    --text-lg: 1.125rem;  /* 18px */
    --text-xl: 1.25rem;   /* 20px */
    --text-2xl: 1.5rem;   /* 24px */
    --text-3xl: 1.875rem; /* 30px */
    --text-4xl: 2.25rem;  /* 36px */
    
    /* Colors */
    --color-primary: rgb(64, 70, 168);
    --color-primary-dark: rgb(54, 60, 148);
    --color-text: #333;
    --color-text-light: #666;
    --color-bg-main: #f8f9fa;
    --color-bg-white: #ffffff;
    --color-border: #e5e7eb;
    --color-shadow: rgba(0, 0, 0, 0.1);
    
    /* Layout */
    --container-max-width: 1000px;
    --container-padding: var(--space-md);
    --border-radius: 8px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: var(--color-text);
    margin: 0;
    padding: 0;
    background-color: var(--color-bg-main);
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

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

header {
    background-color: var(--color-primary);
    color: white;
    padding: 0;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
    position: relative;
    z-index: 1000;
}

header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    min-height: 120px;
    padding: var(--space-sm) var(--container-padding);
    position: relative;
}

.logo {
    display: flex;
    align-items: center;
    z-index: 1001;
}

.logo img {
    margin-right: 10px;
    height: 50px;
    transition: transform 0.2s ease;
}

.logo:hover img {
    transform: scale(1.05);
}

.logo span {
    font-size: var(--text-lg);
    font-weight: 700;
    line-height: 1.2;
    color: white;
    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.1);
}

nav {
    display: flex;
    align-items: center;
}

nav ul {
    list-style-type: none;
    display: flex;
    margin: 0;
    padding: 0;
    align-items: center;
}

nav ul li {
    position: relative;
    margin-left: var(--space-lg);
}

nav ul li a {
    color: white;
    text-decoration: none;
    font-weight: 500;
    font-size: var(--text-sm);
    padding: var(--space-xs) var(--space-sm);
    border-radius: var(--border-radius);
    transition: all 0.3s ease;
    position: relative;
    display: block;
}

nav ul li a:hover {
    background-color: rgba(255, 255, 255, 0.1);
    transform: translateY(-1px);
    text-decoration: none;
}

nav ul li a.active {
    font-weight: 600;
}

nav ul li a.active::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 50%;
    transform: translateX(-50%);
    width: 80%;
    height: 2px;
    background-color: white;
    border-radius: 1px;
}

/* Dropdown styles */
.dropdown {
    position: relative;
}

.dropdown > a {
    display: flex;
    align-items: center;
    gap: var(--space-xs);
}

.dropdown > a::after {
    content: '▼';
    font-size: 0.7em;
    transition: transform 0.3s ease;
    opacity: 0.8;
}

.dropdown:hover > a::after {
    transform: rotate(180deg);
}

.dropdown-content {
    position: absolute;
    top: 100%;
    left: 50%;
    transform: translateX(-50%);
    background-color: white;
    min-width: 280px;
    border-radius: var(--border-radius);
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.15);
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transform: translateX(-50%) translateY(-10px);
    transition: all 0.3s ease;
    border: 1px solid var(--color-border);
    overflow: hidden;
    margin-top: var(--space-xs);
    display: flex;
    flex-direction: column;
}

.dropdown:hover .dropdown-content {
    opacity: 1;
    visibility: visible;
    transform: translateX(-50%) translateY(0);
}

.dropdown-content::before {
    content: '';
    position: absolute;
    top: -8px;
    left: 50%;
    transform: translateX(-50%);
    width: 0;
    height: 0;
    border-left: 8px solid transparent;
    border-right: 8px solid transparent;
    border-bottom: 8px solid white;
}

.dropdown-content li {
    margin: 0;
    border-bottom: 1px solid #f0f0f0;
    display: block;
    width: 100%;
}

.dropdown-content li:last-child {
    border-bottom: none;
}

.dropdown-content a {
    color: var(--color-text);
    padding: var(--space-md) var(--space-lg);
    text-decoration: none;
    display: block;
    font-weight: 400;
    transition: all 0.2s ease;
    border-radius: 0;
    transform: none;
    background-color: transparent;
}

.dropdown-content a:hover {
    background-color: var(--color-bg-main);
    color: var(--color-primary);
    padding-left: calc(var(--space-lg) + 4px);
    transform: none;
}

.dropdown-content a.active {
    background-color: var(--color-primary);
    color: white;
    font-weight: 500;
}

.dropdown-content a.active:hover {
    background-color: var(--color-primary-dark);
    color: white;
    padding-left: calc(var(--space-lg) + 4px);
}

/* Improved focus states for accessibility */
.dropdown-content a:focus {
    outline: 2px solid var(--color-primary);
    outline-offset: -2px;
    background-color: var(--color-bg-main);
    color: var(--color-primary);
}

.dropdown-content a.active:focus {
    outline: 2px solid white;
    outline-offset: -2px;
    background-color: var(--color-primary-dark);
    color: white;
}

/* Keyboard navigation support */
.dropdown:focus-within .dropdown-content {
    opacity: 1;
    visibility: visible;
    transform: translateX(-50%) translateY(0);
}

/* Focus states for main navigation */
nav ul li a:focus {
    outline: 2px solid rgba(255, 255, 255, 0.8);
    outline-offset: 2px;
    background-color: rgba(255, 255, 255, 0.2);
}

/* Logo focus state */
.logo a:focus {
    outline: 2px solid rgba(255, 255, 255, 0.8);
    outline-offset: 2px;
    border-radius: var(--border-radius);
}

/* Ensure logo link styling */
.logo a {
    display: flex;
    align-items: center;
    color: inherit;
    text-decoration: none;
    border-radius: var(--border-radius);
    transition: all 0.2s ease;
    white-space: nowrap;
}

.logo a:hover {
    color: inherit;
    text-decoration: none;
}

/* Mobile hamburger focus state */
.nav-toggle-label:focus-within {
    outline: 2px solid rgba(255, 255, 255, 0.8);
    outline-offset: 2px;
}

/* Skip link for accessibility (add this to HTML if needed) */
.skip-link {
    position: absolute;
    top: -40px;
    left: 6px;
    background: var(--color-primary);
    color: white;
    padding: 8px;
    z-index: 1003;
    text-decoration: none;
    border-radius: 0 0 4px 4px;
    font-weight: 600;
    transition: top 0.2s ease;
}

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

main {
    flex: 1;
    background-color: var(--color-bg-white);
    padding: var(--space-lg) 0;
    margin: var(--space-md) auto;
    max-width: var(--container-max-width);
    width: 90%;
    border-radius: var(--border-radius);
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}

/* Typography - Headers */
h1, h2, h3, h4, h5, h6 {
    color: var(--color-text);
    font-weight: 600;
    line-height: 1.2;
    margin: 0;
}

h1 {
    font-size: var(--text-4xl);
    margin-bottom: var(--space-lg);
}

h2 {
    font-size: var(--text-3xl);
    margin-top: var(--space-xl);
    margin-bottom: var(--space-md);
}

h3 {
    font-size: var(--text-2xl);
    margin-top: var(--space-lg);
    margin-bottom: var(--space-sm);
}

h4 {
    font-size: var(--text-xl);
    margin-top: 0;
    margin-bottom: var(--space-sm);
}

/* First header in sections should have no top margin */
.card h2:first-child,
.container > h1:first-child,
.container > h2:first-child {
    margin-top: 0;
}

/* Typography - Text Content */
p, ul, ol {
    margin: 0 0 var(--space-md) 0;
    line-height: 1.7;
    font-size: var(--text-base);
}

/* Lists */
ul, ol {
    padding-left: var(--space-lg);
}

li {
    margin-bottom: var(--space-xs);
    line-height: 1.6;
}

/* Nested lists */
li ul, li ol {
    margin-top: var(--space-xs);
    margin-bottom: var(--space-xs);
}

/* Links */
a {
    color: var(--color-primary);
    text-decoration: none;
    transition: color 0.2s ease;
}

a:hover {
    color: var(--color-primary-dark);
    text-decoration: underline;
}

footer {
    background-color: #1f2937;
    color: white;
    padding: 2rem 0;
    text-align: center;
    font-size: 0.9rem;
}

/* Components */
.btn {
    display: inline-block;
    padding: var(--space-sm) var(--space-md);
    background-color: var(--color-primary);
    color: white;
    text-decoration: none;
    border-radius: var(--border-radius);
    font-weight: 500;
    font-size: var(--text-base);
    transition: all 0.2s ease;
    border: 2px solid var(--color-primary);
}

.btn:hover {
    background-color: var(--color-primary-dark);
    border-color: var(--color-primary-dark);
    color: white;
    text-decoration: none;
}

.card {
    background: var(--color-bg-white);
    border-radius: var(--border-radius);
    padding: var(--space-lg);
    margin-bottom: var(--space-md);
    box-shadow: 0 2px 4px var(--color-shadow);
    border: 1px solid var(--color-border);
}

/* Utility Classes */
.text-center {
    text-align: center;
}

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

.text-right {
    text-align: right;
}

/* Spacing utilities */
.mt-4 {
    margin-top: var(--space-lg);
}

.mb-4 {
    margin-bottom: var(--space-lg);
}

.mt-8 {
    margin-top: var(--space-2xl);
}

/* Grid System */
.grid-2 {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--space-lg);
}

.grid-3 {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-lg);
}

.grid-4 {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--space-lg);
}

/* Mobile menu styles */
.nav-toggle {
    display: none;
}

.nav-toggle-label {
    display: none;
    cursor: pointer;
    padding: var(--space-sm);
    z-index: 1002;
    position: relative;
    border-radius: var(--border-radius);
    transition: background-color 0.2s ease;
}

.nav-toggle-label:hover {
    background-color: rgba(255, 255, 255, 0.1);
}

.hamburger {
    display: block;
    position: relative;
    width: 24px;
    height: 18px;
}

.hamburger span,
.hamburger span::before,
.hamburger span::after {
    display: block;
    background: white;
    height: 2px;
    width: 100%;
    border-radius: 2px;
    position: absolute;
    transition: all 0.3s ease;
}

.hamburger span {
    top: 50%;
    transform: translateY(-50%);
}

.hamburger span::before,
.hamburger span::after {
    content: '';
}

.hamburger span::before {
    top: -8px;
}

.hamburger span::after {
    top: 8px;
}

/* Hamburger animation */
.nav-toggle:checked + .nav-toggle-label .hamburger span {
    background: transparent;
}

.nav-toggle:checked + .nav-toggle-label .hamburger span::before {
    transform: rotate(45deg);
    top: 0;
}

.nav-toggle:checked + .nav-toggle-label .hamburger span::after {
    transform: rotate(-45deg);
    top: 0;
}

/* Mobile navigation menu */
.mobile-nav {
    display: none;
    position: fixed;
    top: 70px;
    left: 0;
    right: 0;
    background-color: white;
    border-top: 1px solid var(--color-border);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
    z-index: 999;
    max-height: calc(100vh - 70px);
    overflow-y: auto;
}

.nav-toggle:checked ~ .mobile-nav {
    display: block;
}

.mobile-nav ul {
    flex-direction: column;
    padding: var(--space-md) 0;
}

.mobile-nav ul li {
    margin: 0;
    border-bottom: 1px solid var(--color-border);
}

.mobile-nav ul li:last-child {
    border-bottom: none;
}

.mobile-nav ul li a {
    color: var(--color-text);
    padding: var(--space-md) var(--space-lg);
    display: block;
    font-weight: 500;
    border-radius: 0;
    transition: all 0.2s ease;
}

.mobile-nav ul li a:hover,
.mobile-nav ul li a.active {
    background-color: var(--color-bg-main);
    color: var(--color-primary);
    transform: none;
}

.mobile-nav .dropdown-content {
    position: static;
    opacity: 1;
    visibility: visible;
    transform: none;
    box-shadow: none;
    border: none;
    background-color: var(--color-bg-main);
    margin-top: 0;
    border-radius: 0;
}

.mobile-nav .dropdown-content::before {
    display: none;
}

.mobile-nav .dropdown-content li {
    border-bottom: 1px solid var(--color-border);
}

.mobile-nav .dropdown-content a {
    padding-left: calc(var(--space-lg) + var(--space-md));
    color: var(--color-text-light);
    font-size: var(--text-sm);
    background-color: transparent;
}

.mobile-nav .dropdown-content a.active {
    background-color: var(--color-primary);
    color: white;
    font-weight: 500;
}

.mobile-nav .dropdown-content a:hover {
    background-color: rgba(37, 99, 235, 0.1);
    color: var(--color-primary);
    padding-left: calc(var(--space-lg) + var(--space-md) + 4px);
}

.mobile-nav .dropdown-content a.active:hover {
    background-color: var(--color-primary-dark);
    color: white;
    padding-left: calc(var(--space-lg) + var(--space-md) + 4px);
}

/* Hide desktop dropdown on mobile */
.mobile-nav .dropdown:hover .dropdown-content {
    opacity: 1;
    visibility: visible;
    transform: none;
}

/* Responsive Breakpoints */
@media screen and (max-width: 768px) {
    :root {
        --container-padding: var(--space-sm);
        --text-4xl: var(--text-3xl);
        --text-3xl: var(--text-2xl);
        --text-2xl: var(--text-xl);
    }

    header {
        min-height: 70px;
    }

    header .container {
        min-height: 70px;
    }

    /* Show mobile menu toggle */
    .nav-toggle-label {
        display: block;
    }

    /* Hide desktop navigation */
    nav {
        display: none;
    }

    /* Adjust logo size for mobile */
    .logo span {
        font-size: var(--text-base);
    }

    .logo img {
        height: 40px;
    }

    /* Grid responsive behavior */
    .grid-2, .grid-3, .grid-4 {
        grid-template-columns: 1fr;
        gap: var(--space-md);
    }

    /* Spacing adjustments for mobile */
    main {
        width: 95%;
        padding: var(--space-md) 0;
        margin-top: var(--space-md);
    }

    .card {
        padding: var(--space-md);
        margin-bottom: var(--space-sm);
    }

    /* Ensure mobile nav is visible when checkbox is checked */
    .nav-toggle:checked ~ .mobile-nav {
        display: block;
        animation: slideDown 0.3s ease;
    }

    @keyframes slideDown {
        from {
            opacity: 0;
            transform: translateY(-20px);
        }
        to {
            opacity: 1;
            transform: translateY(0);
        }
    }
    
    /* Mobile focus states */
    .mobile-nav a:focus {
        outline: 2px solid var(--color-primary);
        outline-offset: -2px;
        background-color: var(--color-bg-main);
        color: var(--color-primary);
    }
    
    .mobile-nav a.active:focus {
        outline: 2px solid white;
        outline-offset: -2px;
        background-color: var(--color-primary-dark);
        color: white;
    }
    
    /* Prevent body scroll when mobile menu is open */
    .nav-toggle:checked ~ body {
        overflow: hidden;
    }
}

/* Tablet styles */
@media screen and (min-width: 769px) and (max-width: 1024px) {
    :root {
        --container-padding: var(--space-md);
    }
    
    header .container {
        padding: var(--space-sm) var(--space-md);
    }
    
    nav ul li {
        margin-left: var(--space-md);
    }
    
    nav ul li a {
        font-size: var(--text-xs);
        padding: var(--space-xs) var(--space-xs);
    }
    
    .logo span {
        font-size: var(--text-base);
    }
    
    .dropdown-content {
        min-width: 240px;
    }
    
    .grid-3, .grid-4 {
        grid-template-columns: repeat(2, 1fr);
    }
}

/* Large desktop styles */
@media screen and (min-width: 1200px) {
    .dropdown-content {
        min-width: 300px;
    }
    
    nav ul li {
        margin-left: var(--space-xl);
    }
}

/* Form Styles for Calculator and other forms */
.form-group {
    margin-bottom: var(--space-md);
}

.form-label {
    display: block;
    margin-bottom: var(--space-xs);
    font-weight: 600;
    color: var(--color-text);
}

.form-input, .form-select {
    width: 100%;
    padding: var(--space-sm);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    font-size: var(--text-base);
    line-height: 1.5;
    transition: border-color 0.2s ease;
}

.form-input:focus, .form-select:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 2px rgba(37, 99, 235, 0.1);
}

.form-button {
    width: 100%;
    padding: var(--space-sm) var(--space-md);
    background-color: var(--color-primary);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: var(--text-base);
    font-weight: 500;
    transition: background-color 0.2s ease;
}

.form-button:hover {
    background-color: var(--color-primary-dark);
}