body {
    font-family: 'Poppins', sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: space-between;
    min-height: 100vh;
    margin: 0;
    background: linear-gradient(135deg, #1e3c72, #2a5298);
    color: #fff;
    overflow-x: hidden;
    position: relative;
    transition: background 0.3s ease, color 0.3s ease;
}

body.light-theme {
    background: linear-gradient(135deg, #f5f7fa, #c3cfe2);
    color: #333;
}

#particles-js {
    position: absolute;
    width: 100%;
    height: 100%;
    z-index: -1;
}

.logo {
    width: 200px;
    margin: 30px 0;
}

h1 {
    font-size: 2.8em;
    margin-bottom: 40px;
    text-shadow: 3px 3px 6px rgba(0, 0, 0, 0.3);
    letter-spacing: 1.5px;
    text-align: center;
}

.course-list {
    list-style: none;
    padding: 0;
    width: 100%;
    max-width: 600px;
}

.course-list li {
    margin: 30px 0;
    opacity: 0;
    transition: transform 0.3s ease, opacity 0.3s ease;
    position: relative;
}

.course-list a {
    display: flex;
    align-items: center;
    text-decoration: none;
    color: #fff;
    font-size: 1.4em;
    font-weight: 600;
    padding: 20px 30px;
    background: linear-gradient(45deg, #ff6b6b, #ff8e53);
    border-radius: 12px;
    text-align: center;
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.2);
    transition: all 0.4s ease;
    cursor: pointer;
}

.light-theme .course-list a {
    background: linear-gradient(45deg, #ff8e53, #ffb199);
    color: #333;
}

.course-list a:hover {
    background: linear-gradient(45deg, #e55d87, #5fc3e4);
    transform: scale(1.05);
    box-shadow: 0 12px 24px rgba(0, 0, 0, 0.3);
}

.course-list i {
    margin-right: 15px;
    font-size: 1.5em;
}

.course-list a .tooltip {
    visibility: hidden;
    width: 200px;
    background-color: #333;
    color: #fff;
    text-align: center;
    border-radius: 6px;
    padding: 10px;
    position: absolute;
    z-index: 1;
    top: 50%;
    right: 110%;
    transform: translateY(-50%);
    opacity: 0;
    transition: opacity 0.3s;
    font-size: 0.9em;
}

.light-theme .course-list a .tooltip {
    background-color: #555;
}

.course-list a:hover .tooltip {
    visibility: visible;
    opacity: 1;
}

.side-decor {
    position: absolute;
    top: 0;
    width: 80px;
    height: 100%;
    background: linear-gradient(to bottom, rgba(255, 255, 255, 0.1), transparent);
    z-index: 0;
    animation: pulse 4s infinite;
}

.side-decor.left {
    left: 0;
    border-right: 2px solid rgba(255, 255, 255, 0.2);
}

.side-decor.right {
    right: 0;
    border-left: 2px solid rgba(255, 255, 255, 0.2);
}

@keyframes pulse {
    0% { opacity: 0.2; }
    50% { opacity: 0.4; }
    100% { opacity: 0.2; }
}

footer {
    margin-top: 20px;
    padding: 20px;
    text-align: center;
    font-size: 0.9em;
    color: rgba(255, 255, 255, 0.7);
}

.light-theme footer {
    color: rgba(0, 0, 0, 0.7);
}

footer a {
    color: #ff8e53;
    text-decoration: none;
}

.light-theme footer a {
    color: #e55d87;
}

footer a:hover {
    text-decoration: underline;
}

.theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
    background: none;
    border: none;
    color: #fff;
    font-size: 1.5em;
    cursor: pointer;
    transition: color 0.3s ease;
}

.light-theme .theme-toggle {
    color: #333;
}

.loader {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: #1e3c72;
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    opacity: 1;
    transition: opacity 0.5s ease;
}

.loader.hidden {
    opacity: 0;
    pointer-events: none;
}

.spinner {
    border: 8px solid #f3f3f3;
    border-top: 8px solid #ff8e53;
    border-radius: 50%;
    width: 60px;
    height: 60px;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.7);
    opacity: 0;
    pointer-events: none;
    z-index: 1000;
    transition: opacity 0.4s ease;
}

.modal.active {
    opacity: 1;
    pointer-events: auto;
}

.modal-content {
    background: #fff;
    color: #333;
    padding: 30px;
    border-radius: 12px;
    max-width: 500px;
    width: 90%;
    text-align: center;
    position: relative;
    transform: scale(0.9);
    transition: transform 0.3s ease;
}

.modal.active .modal-content {
    transform: scale(1);
}

.light-theme .modal-content {
    background: #f5f7fa;
}

.modal-content h2 {
    margin-top: 0;
}

.modal-content p {
    margin: 20px 0;
}

.modal-content a {
    display: inline-block;
    padding: 10px 20px;
    background: linear-gradient(45deg, #ff6b6b, #ff8e53);
    color: #fff;
    text-decoration: none;
    border-radius: 8px;
    transition: background 0.3s ease;
}

.modal-content a:hover {
    background: linear-gradient(45deg, #e55d87, #5fc3e4);
}

.modal-close {
    position: absolute;
    top: 10px;
    right: 15px;
    font-size: 1.5em;
    cursor: pointer;
    color: #333;
}

@media (max-width: 600px) {
    h1 {
        font-size: 2em;
    }

    .logo {
        width: 120px;
    }

    .course-list a {
        font-size: 1.2em;
        padding: 15px 20px;
    }

    .course-list a .tooltip {
        width: 150px;
        font-size: 0.8em;
        right: 100%;
        transform: translateY(-50%) translateX(-10px);
    }

    .side-decor {
        width: 40px;
    }

    .modal-content {
        width: 95%;
        padding: 20px;
    }
}
