:root {
  --primary: #2563eb;
  --accent: #3b82f6;
  --light: #dbeafe;
}
body {
    font-family: 'Roboto', sans-serif;
    background: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
    position: relative;
    overflow-x: hidden;
    background-image: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100"><rect x="20" y="20" width="60" height="60" fill="none" stroke="%232563eb" stroke-width="0.3" stroke-opacity="0.1"/><rect x="30" y="30" width="40" height="40" fill="none" stroke="%233b82f6" stroke-width="0.3" stroke-opacity="0.1"/></svg>');
}
.header-bg {
    background: var(--primary);
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 20px rgba(37, 99, 235, 0.4);
    border-radius: 0 0 24px 24px;
}
.header-bg::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background:
        radial-gradient(circle at 15% 25%, rgba(255,255,255,0.2) 3%, transparent 10%),
        radial-gradient(circle at 85% 75%, rgba(255,255,255,0.2) 3%, transparent 10%);
    z-index: 1;
    opacity: 0.3;
}
.header-bg::after {
    content: "Học, học nữa, học mãi";
    position: absolute;
    bottom: 2px;
    left: 0;
    right: 0;
    text-align: center;
    color: white;
    font-size: 15px;
    font-weight: bold;
    text-shadow: 0 1px 4px rgba(0,0,0,0.6);
    opacity: 0.95;
    z-index: 2;
}
.search-container {
    margin: 20px auto;
    max-width: 600px;
    position: relative;
}
.search-input {
    width: 100%;
    padding: 10px 40px 10px 15px;
    border: 2px solid var(--primary);
    border-radius: 24px;
    font-size: 16px;
    outline: none;
    transition: border-color 0.3s;
}
.search-input:focus {
    border-color: #1d4ed8;
}
.search-icon {
    position: absolute;
    right: 15px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--primary);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
}
/* CSS cho Countdown (Giữ lại) */
.countdown-box {
    background: rgba(255,255,255,0.9);
    border: 2px solid var(--primary);
    border-radius: 12px;
    min-width: 54px;
    padding: 4px 0;
    font-family: 'Roboto', sans-serif;
    text-align: center;
}
.countdown-label {
    color: var(--primary);
    font-weight: bold;
    font-size: 16px;
}
.countdown-unit {
    color: var(--primary);
    font-size: 12px;
    font-weight: 600;
}
.countdown-main {
    background: var(--primary);
    border-radius: 12px 12px 9px 9px;
    color: white;
    font-weight: 700;
    font-size: 16px;
    padding: 8px 10px;
    min-width: 54px;
    text-align: center;
    letter-spacing: 0.5px;
}

.contact-float {
    position: fixed;
    bottom: 28px;
    right: 32px;
    background: var(--primary);
    color: white;
    font-weight: 700;
    font-size: 18px;
    border-radius: 50px;
    box-shadow: 0 4px 18px rgba(37, 99, 235, 0.3);
    padding: 16px 20px;
    z-index: 50;
    transition: all 0.3s;
    border: 2px solid white;
}
.contact-float:hover {
    background: #1d4ed8;
    transform: scale(1.05);
}
.footer-bg {
    background: linear-gradient(90deg, var(--primary), #60a5fa, #93c5fd);
}
.social-icon {
    color: white;
    transition: all 0.3s ease;
    opacity: 0.8;
}

.social-icon:hover {
    opacity: 1;
    transform: translateY(-3px);
    color: #dbeafe;
}
.special-date-banner {
    background: linear-gradient(90deg, var(--primary), #60a5fa, #93c5fd);
    color: white;
    text-align: center;
    padding: 12px;
    margin-bottom: 20px;
    border-radius: 12px;
    font-weight: 700;
    font-size: 18px;
    text-shadow: 0 1px 3px rgba(0,0,0,0.3);
    animation: pulse 2s infinite;
    position: relative;
    overflow: hidden;
    border: 1px solid rgba(255,255,255,0.3);
    font-family: 'Montserrat', sans-serif;
}
.special-date-banner::after {
    content: "";
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: linear-gradient(
        to bottom right,
        rgba(255,255,255,0) 45%,
        rgba(255,255,255,0.8) 50%,
        rgba(255,255,255,0) 55%
    );
    transform: rotate(30deg);
    animation: shine 3s infinite;
}
@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.02); }
}
@keyframes shine {
    0% { transform: translateX(-100%) rotate(30deg); }
    100% { transform: translateX(100%) rotate(30deg); }
}
.patriot-text {
    font-family: 'Montserrat', sans-serif;
    text-shadow: 0 2px 4px rgba(0,0,0,0.2);
}
@media (max-width: 600px) {
    .special-date-banner {
        font-size: 16px;
        padding: 10px;
    }
    .search-container {
        margin: 15px auto;
    }
    .search-input {
        font-size: 14px;
        padding: 8px 35px 8px 12px;
    }
    .search-icon {
        font-size: 16px;
        right: 12px;
    }
}

/* Thêm vào file style.css */
.subject-btn-active {
    background: linear-gradient(90deg, var(--primary), #60a5fa, #93c5fd);
    color: white;
    text-align: center;
    padding: 12px;
    margin-bottom: 20px;
    border-radius: 12px;
    font-weight: 700;
    font-size: 18px;
    text-shadow: 0 1px 3px rgba(0,0,0,0.3);
    animation: pulse 2s infinite;
    position: relative;
    overflow: hidden;
    border: 1px solid rgba(255,255,255,0.3);
    font-family: 'Montserrat', sans-serif;
}

.subject-btn-active::after {
    content: "";
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: linear-gradient(
        to bottom right,
        rgba(255,255,255,0) 45%,
        rgba(255,255,255,0.8) 50%,
        rgba(255,255,255,0) 55%
    );
    transform: rotate(30deg);
    animation: shine 3s infinite;
}

.subject-btn-inactive {
    background: white;
    color: #374151;
    border: 1px solid #d1d5db;
    padding: 12px;
    border-radius: 12px;
    font-weight: 700;
    font-size: 18px;
    transition: all 0.3s ease;
    font-family: 'Montserrat', sans-serif;
}

.subject-btn-inactive:hover {
    background: #f3f4f6;
    border-color: #93c5fd;
}

.footer-bg ul li a {
    transition: all 0.3s ease;
    display: inline-block;
    text-decoration: none;
    position: relative;
}

.footer-bg ul li a:hover {
    transform: translateY(-3px);
    color: #dbeafe;
    text-decoration: none;
}

.footer-bg ul li a::after {
    content: '';
    position: absolute;
    width: 0;
    height: 2px;
    bottom: -2px;
    left: 50%;
    background-color: #dbeafe;
    transition: all 0.3s ease;
    transform: translateX(-50%);
}

.footer-bg ul li a:hover::after {
    width: 100%;
}