/* ========== 1. Reset cơ bản ========== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: Arial, sans-serif;
}

/* ========== 2. Body ========== */
body {
    background-color: #e8f5e9;
}

/* ========== 3. Header ========== */
header {
    background-color: orange;
    color: white;
    width: 100%;
    top: 0;
    box-shadow: 0 2px 5px rgba(0,0,0,0.2);
    text-align: center;
}
.header-wrapper {
    max-width: 950px;
    margin: 0 auto;
    padding: 10px 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

/* ========== 4. Auth Buttons & Menu Toggle ========== */
.auth-buttons {
    display: flex;
    align-items: center;
    gap: 15px;
}
.auth-buttons a {
    padding: 5px 15px;
    border-radius: 25px;
    text-decoration: none;
    font-weight: bold;
    transition: all 0.3s ease;
}
.register-btn {
    background: #4CAF50;
    color: white;
    border: 2px solid #4CAF50;
}
.login-btn {
    background: #2196F3;
    color: white;
    border: 2px solid #2196F3;
}
.register-btn:hover {
    background: #45a049;
    border-color: #45a049;
}
.login-btn:hover {
    background: #1976D2;
    border-color: #1976D2;
}
.menu-toggle {
    display: none;
    background: none;
    border: none;
    font-size: 24px;
    color: white;
    cursor: pointer;
}

/* ========== 5. Container0 (Tabs) ========== */
.container0 {
    display: flex;
    gap: 10px;
    max-width: 950px;
    margin: 15px auto 0;
    justify-content: flex-start;
    padding-left: 20px;
    flex-wrap: wrap; /* allow wrap on small */
}
.container0 button {
    background-color: #2e7d32;
    color: white;
    border: none;
    padding: 10px 20px;
    font-size: 16px;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.3s;
}
.container0 button:hover {
    background-color: #1b5e20;
}
.container0 button.active {
    background-color: #f1f858;
    color: black;
}

/* ========== 6. Semester Tag ========== */
.semester-tag {
    margin: 20px 0;
}

/* ========== 7. Grid Containers ========== */
.container {
    display: none;
    grid-template-columns: repeat(3, 1fr);
    max-width: 950px;
    margin: 0 auto;
}
.container.active {
    display: grid;
}
.subject-column {
    padding: 20px;
    border-radius: 10px;
}
.subject-column h2 {
    color: #2e7d32;
    margin-bottom: 15px;
    padding-bottom: 10px;
}
.exam-list li {
    margin-bottom: 10px;
}

/* ========== 8. Links & Tags ========== */
a {
    text-decoration: underline;
    color: black;
    cursor: pointer;
}
a:hover {
    color: #1b5e20;
    text-decoration: none;
    font-weight: bold;
}
.new-tag {
    color: #e53935;
    font-weight: bold;
    font-size: 0.9em;
    margin-left: 8px;
    background-color: #fff9e6;
    padding: 2px 8px;
    border-radius: 4px;
    animation: blink 1s infinite ease-in-out;
    border: 1px solid #ffd700;
}
@keyframes blink {
    0% { opacity: 1; }
    50% { opacity: 0.5; }
    100% { opacity: 1; }
}

/* ========== 9. Loading & Error ========== */
.loading, .error {
    padding: 2rem;
    text-align: center;
    font-size: 1.2rem;
    color: #666;
}
.error {
    color: #d32f2f;
}

/* ========== 10. Auth Form Container ========== */
.auth-form-container {
    max-width: 400px;
    margin: 50px auto;
    padding: 20px;
    border: 1px solid #ddd;
    border-radius: 8px;
    background: #fff;
}
.auth-form label {
    display: block;
    margin: 10px 0 5px;
}
.auth-form input {
    width: 100%;
    padding: 8px;
    box-sizing: border-box;
    margin-bottom: 15px;
}
.auth-form .btn {
    width: 100%;
    padding: 10px;
    margin-top: 20px;
    border: none;
    border-radius: 4px;
    background: #4CAF50;
    color: #fff;
    font-size: 16px;
    cursor: pointer;
}
.auth-form .btn:hover {
    background: #45a049;
}

/* ========== 11. Footer ========== */
footer {
    background-color: #e1e1e1;
    color: #444;
    text-align: center;
    padding: 15px;
    width: 100%;
}

/* ========== 12. Media Queries (Mobile) ========== */
@media (max-device-width: 768px) {
    .header-wrapper {
    max-width: unset;
    margin: 0 auto;
    padding: 10px 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}
    /* Header menu */
    .auth-buttons a { display: none; }
    .menu-toggle { display: block; }
    .auth-buttons.open a {
        display: block;
        margin: 10px 0;
    }
    .auth-form-container {
        margin: 30px 20px;
        padding: 20px;
    }

    /* Container0 wrap */
    .container0 {
        justify-content: flex-start;
        padding-left: 0;
        margin: 15px 20px 0;
    }

    /* Grid → list */
    .container {
        display: none; /* vẫn ẩn nếu chưa active */
        grid-template-columns: 1fr;
        margin: 0 20px;
    }
    .container.active {
        display: grid;
    }
    .subject-column {
        padding: 15px;
    }
    .exam-list {
        padding-left: 20px;
    }
}