:root {
    --primary-color: #007bff;
    --secondary-color: #6c757d;
    --background-color: #f8f9fa; /* Main page background */
    --text-color: #333;
    --card-bg: #fff; /* For distinct sections like article or static page content */
    --border-color: #dee2e6;
    --success-color: #28a745;
    --error-color: #dc3545;
    --footer-bg: #e9ecef; /* Footer background */
}

html {
    scroll-behavior: smooth;
    box-sizing: border-box;
}
*, *:before, *:after {
    box-sizing: inherit;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    margin: 0;
    padding: 0;
    background-color: var(--background-color);
    color: var(--text-color);
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* --- Header Navigation (Used on all pages) --- */
.header-nav {
    background-color: var(--primary-color);
    color: white;
    box-shadow: 0 2px 5px rgba(0,0,0,0.15);
    position: sticky;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 10px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.nav-brand {
    font-size: 1.6em;
    font-weight: bold;
    color: white;
    text-decoration: none;
}

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

.nav-links li {
    margin-left: 25px;
}

.nav-links a {
    color: white;
    text-decoration: none;
    font-size: 1em;
    padding: 8px 12px;
    border-radius: 4px;
    transition: background-color 0.2s ease-in-out;
}

.nav-links a:hover,
.nav-links a:focus,
.nav-links a.active-link { /* Style for active link */
    background-color: rgba(255, 255, 255, 0.15);
    font-weight: 500;
}

.nav-toggle {
    display: none;
    background: none;
    border: none;
    padding: 0;
    cursor: pointer;
}
.nav-toggle span {
    display: block;
    width: 25px;
    height: 3px;
    background-color: white;
    margin: 5px 0;
    border-radius: 2px;
    transition: transform 0.3s ease, opacity 0.3s ease;
}
.nav-toggle[aria-expanded="true"] span:nth-child(1) {
    transform: translateY(8px) rotate(45deg);
}
.nav-toggle[aria-expanded="true"] span:nth-child(2) {
    opacity: 0;
}
.nav-toggle[aria-expanded="true"] span:nth-child(3) {
    transform: translateY(-8px) rotate(-45deg);
}

/* --- Page Wrapper & Container (Used on all pages) --- */
.page-wrapper {
    flex-grow: 1;
    width: 100%;
}

.container {
    width: 100%;
    max-width: 960px;
    margin: 0 auto;
    padding: 25px 20px;
}

/* --- Page Main Header (H1 and Subtitle on index.html) --- */
.page-main-header {
    text-align: center;
    margin-bottom: 30px;
    padding-bottom: 15px;
    border-bottom: 1px solid var(--border-color);
}
.page-main-header h1 {
    color: var(--primary-color);
    margin-bottom: 8px;
    font-size: 2.2em;
}
.page-main-header .subtitle {
    color: var(--secondary-color);
    font-size: 1.1em;
}

/* --- Main Content Area (Primarily for index.html calculators) --- */
.main-content {
    /* No specific styling needed unless you want a background distinct from body */
}

/* --- Calculator Sections (index.html) --- */
.calculator-section {
    margin-bottom: 30px;
    padding: 20px 0;
}
.calculator-section h2 {
    color: var(--primary-color);
    font-size: 1.8em;
    margin-top: 0;
    margin-bottom: 25px;
    border-bottom: 1px solid #eee;
    padding-bottom: 10px;
}
.calculator-section h3 {
    color: var(--secondary-color);
    font-size: 1.3em;
    margin-bottom: 15px;
}

.input-section {
    margin-bottom: 25px;
    display: flex;
    flex-direction: column;
    gap: 15px;
}
.input-section label {
    font-weight: bold;
    color: var(--primary-color);
}
.input-section input[type="number"] {
    padding: 12px;
    border: 1px solid var(--border-color);
    border-radius: 5px;
    font-size: 1em;
    width: 100%;
}
.input-section input[type="number"]:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 0.2rem rgba(0, 123, 255, 0.25);
}

.button-group {
    display: flex;
    gap: 10px;
    justify-content: flex-start;
}
.button-group button {
    padding: 10px 20px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1em;
    transition: background-color 0.3s ease;
}
#calculateBtn, #calculateTotalFromCountsBtn {
    background-color: var(--primary-color);
    color: white;
}
#calculateBtn:hover, #calculateTotalFromCountsBtn:hover {
    background-color: #0056b3;
}
#resetBtn, #resetCountsBtn {
    background-color: var(--secondary-color);
    color: white;
}
#resetBtn:hover, #resetCountsBtn:hover {
    background-color: #545b62;
}


.results-section {
    margin-top: 20px;
}

/* Denomination Table - Using simple horizontal scroll for responsiveness */
#denominationTable {
    width: 100%;
    border-collapse: collapse;
    margin-bottom: 15px;
    display: block; 
    overflow-x: auto; 
    -webkit-overflow-scrolling: touch; 
}
#denominationTable th, #denominationTable td {
    border: 1px solid var(--border-color);
    padding: 10px 12px;
    text-align: left;
    white-space: nowrap; 
}
#denominationTable th {
    background-color: #e9ecef;
    font-weight: bold;
    position: sticky; 
    left: 0; 
    z-index: 1; 
}
#denominationTable tbody tr:nth-child(even) {
    background-color: #f8f9fa;
}
#denominationTable tfoot td {
    font-weight: bold;
}
#denominationTable tfoot #remainingAmountDisplay[data-error="true"] {
    color: var(--error-color);
    font-weight: bold;
}


.denominations-input-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 20px 15px;
    margin-bottom: 20px;
}
.denom-input-group {
    display: flex;
    flex-direction: column;
}
.denom-input-group label {
    font-size: 0.9em;
    margin-bottom: 5px;
    color: var(--text-color);
}
.denom-input-group input[type="number"] {
    padding: 10px;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    font-size: 1em;
    width: 100%;
}

.total-sum-display {
    font-size: 1.5em;
    font-weight: bold;
    color: var(--success-color);
    padding: 12px;
    background-color: #e6f7ee;
    border: 1px solid var(--success-color);
    border-radius: 5px;
    text-align: center;
    margin-top: 10px;
}
.error-message {
    color: var(--error-color);
    font-weight: bold;
    margin-top: 10px;
    text-align: center;
}

/* --- Section Divider --- */
.section-divider {
    border: 0;
    height: 1px;
    background-image: linear-gradient(to right, rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.1), rgba(0, 0, 0, 0));
    margin: 40px 0;
}

/* --- Article Content (index.html) --- */
.content-article {
    background-color: var(--card-bg);
    padding: 30px;
    margin-top: 20px;
    margin-bottom: 30px;
    border-radius: 8px;
    box-shadow: 0 3px 10px rgba(0,0,0,0.07);
    line-height: 1.75;
}
.content-article h2 {
    color: var(--primary-color);
    margin-top: 0;
    margin-bottom: 25px;
    font-size: 1.8em;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 10px;
}
.content-article h3 {
    color: var(--secondary-color);
    font-size: 1.5em;
    margin-top: 30px;
    margin-bottom: 15px;
}
.content-article h4 {
    color: var(--primary-color);
    font-size: 1.2em;
    margin-top: 25px;
    margin-bottom: 10px;
}
.content-article p { margin-bottom: 18px; }
.content-article ul, .content-article ol { margin-bottom: 18px; padding-left: 25px; }
.content-article li { margin-bottom: 10px; }
.content-article ul ul { margin-top: 8px; margin-bottom: 12px; }
.content-article strong { color: #222; }
.content-article em { color: var(--secondary-color); font-style: italic; }


/* --- Static Page Content Styling (for about.html, contact.html etc.) --- */
.static-page-header { 
    text-align: center;
    margin-bottom: 30px;
}
.static-page-header h1 {
    color: var(--primary-color);
    font-size: 2em;
}
.static-page-content-wrapper {
    background-color: var(--card-bg);
    padding: 25px 30px;
    border-radius: 8px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.06);
    line-height: 1.7;
}
.static-page-content-wrapper h3 {
    color: var(--secondary-color);
    font-size: 1.4em;
    margin-top: 25px;
    margin-bottom: 10px;
}
.static-page-content-wrapper p { margin-bottom: 15px; }
.static-page-content-wrapper ul { padding-left: 20px; margin-bottom: 15px; }
.static-page-content-wrapper li { margin-bottom: 8px; }
.button-like {
    display: inline-block;
    padding: 10px 18px;
    background-color: var(--primary-color);
    color: white;
    text-decoration: none;
    border-radius: 5px;
    margin-top: 20px;
    font-size: 0.95em;
    transition: background-color 0.2s ease;
}
.button-like:hover { background-color: #0056b3; }


/* --- Footer (Used on all pages) --- */
.site-footer {
    padding: 25px 0;
    border-top: 1px solid var(--border-color);
    font-size: 0.9em;
    color: var(--secondary-color);
    background-color: var(--footer-bg);
    width: 100%;
}
.site-footer .container {
    text-align: center;
}
.site-footer p {
    margin-bottom: 10px;
}
.site-footer .footer-nav a {
    color: var(--primary-color);
    text-decoration: none;
    margin: 0 8px;
}
.site-footer .footer-nav a:hover {
    text-decoration: underline;
}

/* --- Responsive Adjustments --- */
@media (max-width: 768px) {
    .nav-toggle {
        display: block;
    }
    .nav-links {
        display: none;
        flex-direction: column;
        width: 100%;
        background-color: var(--primary-color);
        position: absolute;
        top: 100%;
        left: 0;
        padding: 15px 0;
        box-shadow: 0 3px 5px rgba(0,0,0,0.1);
    }
    .nav-links.active {
        display: flex;
    }
    .nav-links li {
        margin: 10px 0;
        width: 100%;
        text-align: center;
    }
    .nav-links a {
        display: block;
        padding: 12px 20px;
    }

    .container {
        padding-left: 15px;
        padding-right: 15px;
    }

    .page-main-header h1 { font-size: 1.8em; }
    .page-main-header .subtitle { font-size: 1em; }
    .static-page-header h1 { font-size: 1.7em; }


    .calculator-section h2 { font-size: 1.6em; }
    .content-article h2 { font-size: 1.6em; }

    .input-section input[type="number"] {
        font-size: 0.95em;
    }

    .denominations-input-grid {
        grid-template-columns: 1fr;
        gap: 15px;
    }
    .denom-input-group label {
        font-size: 0.85em;
    }

    .button-group {
        flex-direction: column;
    }
    .button-group button {
        width: 100%;
        font-size: 0.95em;
    }

    #denominationTable th, #denominationTable td {
        padding: 8px 10px;
        font-size: 0.9em;
    }
    
    .content-article { padding: 20px 15px; }
    .static-page-content-wrapper { padding: 20px 15px; }
}

@media (max-width: 420px) {
    .nav-brand { font-size: 1.3em;}
    .page-main-header h1 { font-size: 1.6em; }
    .calculator-section h2 { font-size: 1.4em; }
    .content-article h2 { font-size: 1.4em; }
    .static-page-header h1 { font-size: 1.5em; }


    .denom-input-group label {
        font-size: 0.8em;
    }
    .input-section input[type="number"],
    .denom-input-group input[type="number"] {
        padding: 10px;
        font-size: 0.9em;
    }
    .button-group button {
        padding: 10px 15px;
        font-size: 0.9em;
    }
    #denominationTable th, #denominationTable td {
        font-size: 0.85em;
        padding: 6px 8px;
    }
}