:root {
    --bg-color: #050507;
    --card-bg: rgba(255, 255, 255, 0.04);
    --border: rgba(255, 255, 255, 0.1);
    --accent: #00f2ea;
    --text-main: #ffffff;
    --text-dim: #94a3b8;
}

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

body {
    background-color: var(--bg-color);
    color: var(--text-main);
    font-family: 'Inter', sans-serif;
    min-height: 100vh;
}

.background-grid {
    position: fixed;
    top: 0; left: 0; width: 100%; height: 100%;
    background-image: 
        linear-gradient(rgba(255, 255, 255, 0.02) 1px, transparent 1px),
        linear-gradient(90deg, rgba(255, 255, 255, 0.02) 1px, transparent 1px);
    background-size: 40px 40px;
    z-index: -1;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 40px 20px;
}

/* Header */
header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 50px;
}

h1 {
    font-family: 'Orbitron', sans-serif;
    font-size: 2rem;
    letter-spacing: 1px;
}

.highlight { color: var(--accent); }

.subtitle {
    color: var(--text-dim);
    font-size: 0.9rem;
    margin-top: 4px;
}

.date-area {
    text-align: right;
    font-family: 'Orbitron', sans-serif;
    font-size: 0.8rem;
    border-left: 2px solid var(--accent);
    padding-left: 15px;
}

.date-box span { display: block; }
#current-time { color: var(--accent); font-weight: bold; font-size: 1.1rem; }

/* Grid System: 2 for Mobile, 3 for PC */
.app-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
}

@media (min-width: 900px) {
    .app-grid { grid-template-columns: repeat(3, 1fr); gap: 30px; }
}

/* Card Styling */
.card {
    background: var(--card-bg);
    border: 1px solid var(--border);
    border-radius: 12px;
    overflow: hidden;
    text-decoration: none;
    color: inherit;
    transition: all 0.3s ease;
    display: flex;
    flex-direction: column;
    backdrop-filter: blur(8px);
}

.card:hover {
    transform: translateY(-8px);
    border-color: var(--accent);
    background: rgba(255, 255, 255, 0.07);
    box-shadow: 0 15px 30px rgba(0, 0, 0, 0.5);
}

.card-visual {
    height: 100px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2.5rem;
    background: #1a1a1a;
}

.card-body { padding: 20px; flex-grow: 1; display: flex; flex-direction: column; }

.tag {
    font-size: 0.65rem;
    font-weight: bold;
    text-transform: uppercase;
    margin-bottom: 10px;
    padding: 2px 8px;
    border-radius: 4px;
    width: fit-content;
    background: rgba(255,255,255,0.05);
}

.tag.math { color: #00f2ea; }
.tag.history { color: #ff0050; }
.tag.logic { color: #cc00ff; }

h3 { font-family: 'Orbitron', sans-serif; font-size: 1.1rem; margin-bottom: 10px; }

p { font-size: 0.85rem; color: var(--text-dim); margin-bottom: 20px; line-height: 1.5; flex-grow: 1; }

.card-action {
    display: flex;
    justify-content: space-between;
    font-size: 0.75rem;
    font-weight: bold;
    color: var(--accent);
    padding-top: 15px;
    border-top: 1px solid var(--border);
}

.arrow { transition: transform 0.2s; }
.card:hover .arrow { transform: translateX(5px); }

.card.locked { opacity: 0.4; cursor: not-allowed; }

/* Footer */
footer { margin-top: 80px; text-align: center; }
.footer-line { height: 1px; background: linear-gradient(90deg, transparent, var(--border), transparent); margin-bottom: 20px; }
footer p { font-family: 'Orbitron', sans-serif; font-size: 0.7rem; letter-spacing: 2px; }