/* ========================================================================
   Sticky Header-Enhanced Mobile-First Two-Column Layout (Light Mode Only)
   ======================================================================== */

/* 1. Variables */
:root {
    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
    --font-serif: 'Georgia', serif;

    --color-text: #333;
    --color-bg: #f4f4f9;
    --color-link: #007bff;
    --color-link-hover: #0056b3;
    --color-button-bg: #004d40;
    --color-button-bg-hover: #00332c;
    --color-button-text: #fff;

    --color-heading-1: #1a5276;
    --color-heading-2: #3498db;
    --color-heading-3: #6c7a89;
    --color-heading-4: #9b59b6;
    --color-heading-5: #2ecc71;
    --color-heading-6: #d67344;

    --color-column-left: #f0f8ff;
    --color-column-right: #f5f5dc;
    --color-border: #ccc;

    --spacing-s: 1rem;
    --spacing-m: 1.5rem;

    --font-size-base: 13.5px;
    --line-height-base: 1.6;
}

/* 2. Reset & Base */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html, body {
    min-height: 100vh;
    font-family: var(--font-sans);
    font-size: var(--font-size-base);
    line-height: var(--line-height-base);
    color: var(--color-text);
    background: var(--color-bg);
}

body {
    padding: var(--spacing-s);
}

/* 3. Layout */
.container {
    display: flex;
    flex-direction: column;
    max-width: 960px;
    margin: 0 auto;
}

.column {
    padding: var(--spacing-s);
    -webkit-overflow-scrolling: touch;
}

.column-left {
    background: var(--color-column-left);
    border-bottom: 1px solid var(--color-border);
    flex: 1;
}

.column-right {
    background: var(--color-column-right);
    flex: 4;
}

/* 4. Typography & Sticky Headers */

h1, h2, h3, h4, h5, h6 {
    font-family: var(--font-serif);
    line-height: 1.2;
    margin-bottom: var(--spacing-s);
    text-align: left;
    /* Removed sticky positioning */
    /* position: sticky;
    top: 0;
    z-index: 5;
    background: inherit;
    padding-top: var(--spacing-s); */
}



h1 { color: var(--color-heading-1); font-size: 2.5rem; border-bottom: 2px solid var(--color-heading-1); padding-bottom: 5px; }
h2 { color: var(--color-heading-2); font-size: 2rem; border-bottom: 2px solid var(--color-heading-2); padding-bottom: 5px; }
h3 { color: var(--color-heading-3); font-size: 1.75rem; border-bottom: 2px solid var(--color-heading-3); padding-bottom: 5px; }
h4 { color: var(--color-heading-4); font-size: 1.5rem; }
h5 { color: var(--color-heading-5); font-size: 1.25rem; }
h6 { color: var(--color-heading-6); font-size: 1rem; }

p {
    margin-bottom: var(--spacing-s);
}

/* 5. Links & Media */
a {
    color: var(--color-link);
    text-decoration: none;
    transition: color 0.3s ease;
}

a:hover, a:focus {
    color: var(--color-link-hover);
    text-decoration: underline;
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

ul, ol {
    margin-bottom: var(--spacing-s);
    padding-left: 1.5rem;
}

li {
    margin-bottom: 0.5rem;
    line-height: var(--line-height-base);
}

/* 6. Buttons */
button, input[type="submit"], .button {
    display: inline-block;
    padding: 0.75rem var(--spacing-m);
    font-size: 1rem;
    font-weight: bold;
    cursor: pointer;
    border-radius: 0.5rem;
    border: none;
    background: var(--color-button-bg);
    color: var(--color-button-text);
    transition: background 0.3s ease, transform 0.2s ease;
}

button:hover, input[type="submit"]:hover, .button:hover {
    background: var(--color-button-bg-hover);
    transform: translateY(-2px);
}

button:focus, input[type="submit"]:focus, .button:focus {
    outline: 2px solid var(--color-link);
    outline-offset: 2px;
}

/* 7. Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    * {
        transition: none !important;
        animation: none !important;
    }
}

/* 8. Media Queries */
/* Tablet+ */
@media (min-width: 600px) {
    body { font-size: 17px; }
    h1 { font-size: 3rem; }
    h2 { font-size: 2.5rem; }
    h3 { font-size: 2rem; }
    h4 { font-size: 1.75rem; }
    h5 { font-size: 1.5rem; }
    h6 { font-size: 1.25rem; }
}

/* Desktop+ */
@media (min-width: 960px) {
    body { font-size: 18px; }
    .container { flex-direction: row; }
    .column-left { border-right: 1px solid var(--color-border); border-bottom: none; }
    h1 { font-size: 3.5rem; }
    h2 { font-size: 3rem; }
    h3 { font-size: 2.5rem; }
    h4 { font-size: 2rem; }
    h5 { font-size: 1.75rem; }
    h6 { font-size: 1.5rem; }
}