@import url('https://fonts.googleapis.com/css2?family=Orbitron:wght@400;700&display=swap');

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

body { 
    background: #000; 
    color: #fff; 
    font-family: 'Orbitron', sans-serif; 
    overflow: hidden; 
    height: 100vh;
    width: 100vw;
}

header nav {
    position: absolute;
    top: 20px; left: 0; width: 100%;
    display: flex; justify-content: center; gap: 30px;
    z-index: 2000; 
}
header nav a {
    color: #00f2ff; text-decoration: none; font-size: 0.9em;
    letter-spacing: 2px; text-shadow: 0 0 10px rgba(0, 242, 255, 0.7);
}

.bg-slider {
    position: fixed;
    top: 0; left: 0; width: 100%; height: 100%;
    z-index: 1;
}
.bg-slide {
    position: absolute;
    top: 0; left: 0; width: 100%; height: 100%;
    background-size: cover;
    background-position: center;
    opacity: 0;
    transition: opacity 1.2s ease-in-out; 
}
.bg-slide.active { opacity: 1; }

.color-overlay {
    position: absolute;
    top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(255, 0, 100, 0.3); 
    mix-blend-mode: overlay;
    transition: background 1.5s ease-in-out; 
}

.dark-overlay {
    position: absolute;
    top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0, 0, 0, 0.5);
}



.main-content {
    position: absolute;
    top: 50%; left: 50%;
    transform: translate(-50%, -50%);
    text-align: center;
    z-index: 1000;
    width: 80%;
}


.year {
    font-size: 1.5em;
    color: #fff;
    letter-spacing: 10px;
    margin-bottom: 15px;
    opacity: 0;
    transform: translateY(-50px); /* উপরে থেকে নামবে */
    animation: slideDown 1s cubic-bezier(0.25, 0.46, 0.45, 0.94) 0.2s forwards;
    text-shadow: 0 0 10px #fff;
    border-top: 1px solid #fff;
    border-bottom: 1px solid #fff;
    display: inline-block;
    padding: 5px 20px;
}


.title { 
    font-size: 5em; 
    font-weight: bold; 
    text-shadow: 0 0 20px #ff00ff, 0 0 40px #ff00ff; 
    margin-bottom: 10px;
    opacity: 0;
    transform: translateX(-100px); /* বাম পাশ থেকে আসবে */
    animation: slideRight 1s cubic-bezier(0.25, 0.46, 0.45, 0.94) 0.5s forwards;
}


.topic { 
    font-size: 5em; 
    font-weight: bold; 
    color: #00f2ff; 
    text-shadow: 0 0 20px #00f2ff;
    margin-bottom: 20px;
    opacity: 0;
    transform: translateX(100px); 
    animation: slideLeft 1s cubic-bezier(0.25, 0.46, 0.45, 0.94) 0.8s forwards;
}

.des { 
    font-size: 1.2em; 
    max-width: 600px; 
    margin: 0 auto 30px auto; 
    line-height: 1.5; 
    color: #ccc;
    opacity: 0;
    animation: fadeInUp 1s ease 1.1s forwards;
}


@keyframes slideDown {
    to { opacity: 1; transform: translateY(0); }
}
@keyframes slideRight {
    to { opacity: 1; transform: translateX(0); }
}
@keyframes slideLeft {
    to { opacity: 1; transform: translateX(0); }
}
@keyframes fadeInUp {
    from { opacity: 0; transform: translateY(30px); }
    to { opacity: 1; transform: translateY(0); }
}

/* ==========================================
   বাটন এবং বটম কন্ট্রোলস
   ========================================== */

.buttons { 
    display: flex; 
    gap: 20px; 
    justify-content: center;
    opacity: 0;
    animation: fadeInUp 1s ease 1.4s forwards;
}
.buttons button {
    padding: 14px 35px;
    background: rgba(0, 0, 0, 0.6); border: 1px solid #a3ff00; color: #fff; 
    font-family: 'Orbitron', sans-serif; font-size: 0.9em; letter-spacing: 2px;
    cursor: pointer; transition: all 0.3s ease;
    box-shadow: 0 0 8px #a3ff00, inset 0 0 8px rgba(163, 255, 0, 0.1);
}
.buttons button:hover {
    background: #a3ff00; color: #000;
    box-shadow: 0 0 25px #a3ff00, 0 0 50px rgba(163, 255, 0, 0.4);
}

.bottom-controls {
    position: absolute;
    bottom: 40px; left: 0; width: 100%;
    display: flex; justify-content: space-between; align-items: center;
    padding: 0 5%; box-sizing: border-box;
    z-index: 1000;
}
.arrows { display: flex; gap: 15px; }
.arrows button {
    width: 60px; height: 60px; border-radius: 50%; background: rgba(0, 242, 255, 0.15);
    border: 2px solid #00f2ff; color: #00f2ff; cursor: pointer; font-size: 1.5em; transition: 0.3s;
}
.arrows button:hover { background: rgba(0, 242, 255, 0.4); box-shadow: 0 0 15px #00f2ff; }

.credits { color: #00f2ff; font-size: 0.85em; opacity: 0.8; text-align: center; text-shadow: 0 0 8px rgba(0, 242, 255, 0.5); }

@media (max-width: 768px) {
    .year { font-size: 1em; letter-spacing: 5px; padding: 3px 10px; }
    .title, .topic { font-size: 2.2em; }
    .des { font-size: 0.9em; }
    .bottom-controls { flex-direction: column; gap: 15px; bottom: 20px; }
    .credits { font-size: 0.6em; }
    .arrows button {
        width: 70px;
        height: 70px;
        font-size: 1.8em;
    }
}