* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --bg: #0f172a;
    --panel: #111c2b;
    --panel-2: #162235;
    --stroke: #2c3f58;
    --text: #ffffff;
    --muted: #cfdeed;
    --accent: #ffd900;
    --accent-strong: #a58300;
}

html {
    scroll-behavior: smooth;
}

body {
    background-color: var(--bg);
    font-family: system-ui, -apple-system, 'Segoe UI', Roboto, 'Helvetica Neue', sans-serif;
    line-height: 1.5;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

main {
    flex: 1;
    display: flex;
    flex-direction: column;
}

a {
    text-decoration: none;
    color: inherit;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 24px;
}

header {
    background: rgba(0, 0, 0, 0.9);
    border-bottom: 1px solid rgba(255, 255, 255, 0.25);
    padding: 12px 32px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    flex-wrap: wrap;
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(8px);
}

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
}

.logo img {
    width: 40px;
    height: 40px;
    object-fit: contain;
}

.logo h1 {
    font-size: 30px;
    font-weight: 700;
    background: linear-gradient(135deg, #ffe608, #e205ff);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
}

nav ul {
    display: flex;
    gap: 40px;
    list-style: none;
}

nav ul li {
    position: relative;
}

nav ul li a {
    color: var(--text);
    font-size: 1.05rem;
    font-weight: 600;
    padding: 8px 0;
    border-bottom: 2px solid transparent;
    transition: color 0.2s ease, border-color 0.2s ease;
}

nav ul li a:hover {
    color: var(--accent);
    border-bottom-color: var(--accent);
}

.nav-item {
    position: relative;
}

.mega-menu {
    position: absolute;
    top: 120%;
    right: 0;
    width: max-content;
    max-width: 90vw;
    background: #0b1220;
    border: 1px solid var(--stroke);
    border-radius: 16px;
    padding: 8px;
    display: none;
    flex-direction: column;
    gap: 6px;
    box-shadow: 0 12px 26px rgba(0, 0, 0, 0.42);
}

.nav-item:hover .mega-menu,
.mega-menu:hover {
    display: flex;
    align-items: flex-start;
}

.menu-column {
    background: #13233a;
    border-radius: 12px;
    padding: 8px 12px;
    width: fit-content;
    border: 1px solid #233a57;
    transition: transform 0.2s ease, background-color 0.2s ease, border-color 0.2s ease;
    cursor: pointer;
}

.menu-column a {
    display: block;
}

.menu-column:hover {
    background: #1a2e49;
    border-color: #355a84;
    transform: translateY(-2px);
}

.menu-column h3 {
    color: #e8f0ff;
    font-size: 1rem;
    margin: 0;
    white-space: nowrap;
    font-weight: 600;
}

.page-section {
    display: none;
    padding: 52px 24px;
    background: black;
    flex: 1;
}

.page-section.active-section {
    display: block;
}

.hero {
    background: black;
}

.hero-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 48px;
    align-items: center;
}

.hero-content h1 {
    color: var(--text);
    font-size: 4rem;
    font-weight: 800;
    margin-bottom: 16px;
}

.hero-content p {
    color: #ffffffc9;
    font-size: 1.4rem;
    max-width: 500px;
}

.hero-image {
    background-image: url('Cat.gif');
    background-repeat: no-repeat;
    background-position: center;
    background-size: contain;
    width: 100%;
    min-height: 400px;
    border-radius: 24px;
}

#about h2,
#activities h2,
#exercise3 h2,
#exercise4 h2 {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--accent);
    border-left: 8px solid var(--accent);
    padding-left: 20px;
    margin-bottom: 30px;
    max-width: 1200px;
    margin-left: auto;
    margin-right: auto;
}

#about p {
    color: #ffffffd8;
    font-size: 1.2rem;
    line-height: 1.7;
    max-width: 1200px;
    margin: auto;
    padding-left: 28px;
}

.activity-card {
    background: var(--panel);
    border: 1px solid var(--stroke);
    border-radius: 32px;
    padding: 2rem 2.5rem;
    width: 100%;
    max-width: 750px;
    margin: 0 auto 2rem auto;
    color: var(--text);
    box-shadow: 0 15px 30px -10px #000000cc;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.activity-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 18px 34px -12px #000000d9;
}

.activity-card h3 {
    color: #ffd966;
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 1rem;
}

.activity-card p {
    color: var(--muted);
    font-size: 1.05rem;
    margin-bottom: 1.5rem;
}

.run-btn {
    background: #0b1220;
    border: 1px solid var(--stroke);
    color: #e8f0ff;
    font-weight: 650;
    font-size: 1.05rem;
    padding: 0.8rem 2rem;
    border-radius: 12px;
    cursor: pointer;
    transition: transform 0.15s, background-color 0.15s, border-color 0.15s;
    box-shadow: none;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}

.run-btn:hover {
    background: #0f1a2c;
    border-color: #3a5272;
    transform: translateY(-1px);
}

input {
    padding: 0.7rem 0.9rem;
    border-radius: 10px;
    border: 1px solid var(--stroke);
    background: #020617;
    color: white;
    width: 100%;
    transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

input:focus {
    outline: none;
    border-color: #48658b;
    box-shadow: 0 0 0 3px rgba(72, 101, 139, 0.25);
}

.input-group {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-bottom: 1rem;
}

#dynamicImage {
    width: 100%;
    max-width: 200px;
    border-radius: 12px;
    margin-bottom: 1rem;
}

#itemList,
#todoList {
    margin-top: 1rem;
    padding-left: 1.5rem;
    color: var(--muted);
}

.grade-layout {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 1.5rem;
    margin-top: 2rem;
}

.grade-column {
    background: var(--panel-2);
    border: 1px solid var(--stroke);
    border-radius: 20px;
    padding: 1rem;
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.03);
}

.grade-column h4 {
    color: var(--accent);
    margin-bottom: 1rem;
}

.grade-column > input {
    margin-bottom: 0.65rem;
}

.grade-column > .run-btn {
    width: 100%;
    justify-content: center;
    margin-bottom: 0.75rem;
}

.grade-row {
    display: flex;
    gap: 10px;
    margin-bottom: 0.6rem;
}

.grade-row input {
    width: 50%;
}

.grade-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    margin-top: 2rem;
}

#calcGradeBtn {
    background: var(--accent);
    color: #111827;
    border: none;
    font-weight: 800;
    box-shadow: 0 6px 16px rgba(255, 217, 0, 0.28);
}

#calcGradeBtn:hover {
    background: #ffe75a;
    transform: translateY(-1px);
}

.grade-results {
    margin-top: 1.5rem;
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

#finalGradeOutput,
#gradeEquivalentOutput {
    color: #e8f0ff;
    font-weight: 700;
    margin-bottom: 0.5rem;
    background: linear-gradient(180deg, #0f1a2d 0%, #0b1220 100%);
    border: 1px solid var(--stroke);
    border-radius: 10px;
    padding: 0.55rem 0.9rem;
    min-width: 160px;
}

footer {
    background: black;
    border-top: 1px solid #2d3748;
    padding: 28px 24px;
    text-align: center;
    color: #f3f8fff1;
    margin-top: auto;
}

@media (max-width: 768px) {

    header {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
    }

    nav {
        width: 100%;
    }

    nav ul {
        flex-wrap: wrap;
        gap: 20px;
    }

    .hero-grid {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .hero-content h1 {
        font-size: 2.8rem;
    }

    .hero-content p {
        margin: auto;
    }

    .hero-image {
        min-height: 250px;
    }

    .activity-card {
        padding: 1.5rem;
    }

    .activity-card h3 {
        font-size: 1.5rem;
    }

    #about h2,
    #activities h2,
    #exercise3 h2,
    #exercise4 h2 {
        font-size: 2rem;
    }

}