:root {
    --blue: #007bff;
    --light-bg: #ffffff;
    --light-text: #111111;
    --dark-bg: #0d0d0d;
    --dark-text: #f1f1f1;
    --light-card: #f5f5f5;
    --dark-card: #1a1a1a;
    --shadow: rgba(0, 0, 0, 0.15);
    --radius: 12px;
    --transition: 0.3s ease;
}

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

body {
    font-family: "Inter", "Segoe UI", Arial, sans-serif;
    background-color: var(--light-bg);
    color: var(--light-text);
    line-height: 1.6;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    transition: background-color var(--transition), color var(--transition);
}

/* Header */
header {
    display: flex;
    flex-direction: column; /* stacked layout */
    align-items: center;
    gap: 0.75rem;
    padding: 1rem;
    background: var(--blue);
    color: #fff;
    box-shadow: 0 2px 6px var(--shadow);
}

header h1 {
    font-size: 1.8rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin: 0;
}

/* Navigation */
nav {
    display: flex;
    align-items: center;
    gap: 1.5rem;
}

/* Nav Links */
nav a {
    position: relative;
    font-weight: 600;
    text-decoration: none;   /* kill default underline */
    color: inherit;
    padding: 0.25rem 0;
    transition: color 0.3s ease;
}

/* Animated underline */
nav a::after {
    content: "";
    position: absolute;
    left: 50%;
    bottom: 0;
    width: 0%;
    height: 2px;
    background: currentColor;
    border-radius: 2px;
    transition: width 0.3s ease, left 0.3s ease;
}
nav a:hover::after {
    width: 100%;
    left: 0;
}

/* Hover colors */
body:not(.dark) nav a:hover {
    color: var(--blue);
}
body.dark nav a:hover {
    color: #66b2ff;
}

/* Active link support */
nav a.active {
    color: var(--blue);
}
body.dark nav a.active {
    color: #66b2ff;
}
nav a.active::after {
    width: 100%;
    left: 0;
}

/* Theme toggle button */
#themeToggle {
    background: #fff;
    color: var(--blue);
    border: none;
    padding: 0.5rem 1rem;
    border-radius: var(--radius);
    font-weight: bold;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.3s ease, background 0.3s ease, color 0.3s ease;
}
#themeToggle:hover {
    transform: scale(1.08);
    box-shadow: 0 0 10px rgba(0, 123, 255, 0.6);
}
body.dark #themeToggle {
    background: var(--dark-card);
    color: #fff;
    border: 1px solid #fff;
}

/* Main Content */
main {
    flex: 1;
    padding: 2rem;
    max-width: 900px;
    margin: 2rem auto;
    border-radius: var(--radius);
    background: var(--light-card);
    box-shadow: 0 8px 20px rgba(0,0,0,0.1);
    transition: background var(--transition), color var(--transition);
}

main h1 {
    margin-bottom: 1rem;
    font-size: 2rem;
}

main a {
    display: inline-block;
    transition: transform var(--transition);
}
main a:hover {
    transform: scale(1.05);
}

/* Footer */
footer {
    background: var(--blue);
    color: #fff;
    text-align: center;
    padding: 1rem;
    font-size: 0.85rem;
    opacity: 0.95;
}

/* Dark Mode */
body.dark {
    background-color: var(--dark-bg);
    color: var(--dark-text);
}
body.dark main {
    background: var(--dark-card);
}
body.dark footer {
    background: #111;
}