/* Basic Reset & Font */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Inter', sans-serif;
    background: linear-gradient(135deg, #f5f7fa 0%, #e0e8f0 100%);
    color: #333;
    line-height: 1.6;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

header {
    padding: 24px 40px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.6rem;
    font-weight: 700;
    color: #2c3e50;
}

/* Hero Section */
.hero-fold {
    flex-grow: 1;
    display: flex;
    justify-content: center;
    padding-top: 80px;
    padding-bottom: 40px;
    text-align: center;
}

.center-content {
    max-width: 700px;
    width: 100%;
    padding: 0 20px;
}

h1 {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: 1.2rem;
    color: #1a237e;
    line-height: 1.2;
}

p {
    font-size: 1rem;
    color: #546e7a;
    margin: 0 auto 2.5rem;
    max-width: 540px;
}

/* Input & Button */
.input-group {
    position: relative;
}

#youtubeUrl {
    width: 100%;
    padding: 18px 25px;
    font-size: 1rem;
    border: 1px solid #b0bec5;
    border-radius: 10px;
    margin-bottom: 1.2rem;
    transition: border-color 0.3s ease, box-shadow 0.3s ease;
}

#youtubeUrl:focus {
    outline: none;
    border-color: #007bff;
    box-shadow: 0 0 0 4px rgba(0, 123, 255, 0.15);
}

#submitBtn {
    padding: 16px 35px;
    font-size: 1.1rem;
    font-weight: 600;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: background-color 0.3s ease, transform 0.2s ease;
}

#submitBtn:hover:not(:disabled) {
    background-color: #0056b3;
    transform: translateY(-2px);
}

#submitBtn:disabled {
    background-color: #cccccc;
    cursor: not-allowed;
}

/* Loader */
.loader {
    border: 4px solid #f3f3f3;
    border-top: 4px solid #007bff;
    border-radius: 50%;
    width: 30px;
    height: 30px;
    animation: spin 1s linear infinite;
    margin: 20px auto 0;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Error message */
.error-message {
    color: #d9534f;
    font-size: 0.9rem;
    margin-top: 10px;
    min-height: 1.2em;
}

/* Utility */
.hidden {
    display: none;
}

/* Responsive */
@media (max-width: 768px) {
    h1 {
        font-size: 2.2rem;
    }
    p {
        font-size: 1rem;
    }
    header {
        padding: 15px 20px;
    }
}

@media (max-width: 768px) {
    h1 {
        font-size: 2.2rem;
    }

    p {
        font-size: 1rem;
    }

    header {
        padding: 15px 20px;
    }

    .input-group {
        display: flex;
        flex-direction: column;
        align-items: stretch;
        gap: 12px;
    }

    #youtubeUrl {
        font-size: 1rem;
        padding: 14px 20px;
    }

    #submitBtn {
        font-size: 1rem;
        padding: 14px 20px;
        width: 100%;
    }
}