* {
    box-sizing: border-box;
}

.lessons-header {
    text-align: center;
    margin-bottom: 3rem;
    max-width: 1200px;
    padding: 0 var(--margin);
}

.lessons-header .title {
    font-family: var(--font-family-serif), serif;
    font-size: 3.5rem;
    line-height: 1.2;
    font-weight: 400;
    margin-bottom: 1.5rem;
}

.lessons-header .description {
    font-size: 1.35rem;
    line-height: 1.6;
    max-width: 800px;
    margin: 0 auto;
    color: color-mix(in srgb, var(--border-color) 50%, black);
}

.back-link {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    color: var(--primary-color);
    text-decoration: none;
    font-size: 1rem;
    margin-bottom: 2.5rem;
    transition: transform 0.2s;
}

.back-link:hover {
    transform: translateX(-4px);
}

.payment-form {
    width: 100%;
    max-width: 1200px;
    margin: 2rem auto;
    padding: 4rem 5rem;
    background: color-mix(in srgb, var(--background-color) 97%, var(--font-color));
    border-radius: 32px;
    box-shadow: inset 0 0 0 1px rgba(0,0,0,0.03);
}

.form-section {
    margin-bottom: 4rem;
}

.section-title {
    font-family: var(--font-family-serif), serif;
    font-size: 2rem;
    font-weight: 400;
    margin-bottom: 2.5rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 1rem;
    color: var(--font-color);
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-row {
    display: flex;
    gap: 2rem;
    margin-bottom: 1rem;
}

.form-row .form-group {
    flex: 1;
    max-width: none;
}

@media (max-width: 600px) {
    .form-row {
        flex-direction: column;
        gap: 0;
    }
}

.form-group label {
    display: block;
    margin-bottom: 0.6rem;
    font-weight: 400;
    font-size: 0.95rem;
    color: color-mix(in srgb, var(--font-color) 70%, black);
}

.form-group input {
    width: 100%;
    padding: 14px 18px;
    border: 1px solid var(--border-color);
    border-radius: 12px;
    font-size: 1rem;
    font-family: inherit;
    transition: all 0.2s ease;
    -webkit-appearance: none;
    background: white;
}

.form-group input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px color-mix(in srgb, var(--primary-color) 15%, transparent);
}

.lesson-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1.5rem;
}

.lesson-group-title {
    grid-column: 1 / -1;
    font-size: 1.1rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: color-mix(in srgb, var(--font-color) 40%, black);
    margin-top: 1.5rem;
    margin-bottom: 1rem;
}

.highlight {
    color: #16a34a;
    font-weight: 700;
}

.lesson-card {
    position: relative;
    height: 100%;
}

.lesson-card input[type="radio"] {
    position: absolute;
    opacity: 0;
    width: 0;
    height: 0;
}

.card-content {
    display: flex;
    flex-direction: column;
    height: 100%;
    padding: 1.75rem;
    border: 1.5px solid var(--border-color);
    border-radius: 16px;
    cursor: pointer;
    transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
    background: white;
}

.lesson-card input[type="radio"]:checked + .card-content {
    border-color: var(--primary-color);
    border-width: 2px;
    background: white;
    box-shadow: 0 10px 25px color-mix(in srgb, var(--primary-color) 10%, transparent);
    transform: translateY(-2px);
}

.lesson-card:hover .card-content {
    border-color: color-mix(in srgb, var(--border-color) 40%, var(--primary-color));
}

.card-title {
    font-size: 1.5rem;
    margin: 0.5rem 0 0.25rem;
    font-family: var(--font-family-serif), serif;
    line-height: 1.2;
    font-weight: 400;
    color: var(--font-color);
}

.card-info {
    font-size: 1rem;
    color: color-mix(in srgb, var(--font-color) 60%, black);
    margin-bottom: 1.5rem;
}

.card-price {
    font-size: 1.75rem;
    font-weight: 700;
    margin-top: auto;
    display: flex;
    align-items: baseline;
    gap: 8px;
    color: var(--font-color);
}

.old-price {
    font-size: 1.1rem;
    text-decoration: line-through;
    color: color-mix(in srgb, var(--border-color) 80%, black);
    font-weight: 400;
}

.unit-price {
    font-size: 0.95rem;
    color: #16a34a;
    font-weight: 600;
    margin-top: 4px;
}

.badge {
    display: inline-block;
    padding: 4px 10px;
    border-radius: 6px;
    font-size: 0.75rem;
    text-transform: uppercase;
    font-weight: 700;
    letter-spacing: 0.05em;
    background: #f3f4f6;
    color: #4b5563;
    align-self: flex-start;
    margin-bottom: 0.75rem;
}

.badge.sale {
    background: #dcfce7;
    color: #166534;
}

.form-footer {
    text-align: center;
    margin-top: 4rem;
    padding-top: 2rem;
    padding-bottom: 4rem;
    border-top: 1px solid var(--border-color);
}

.buy-button {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: 20px 64px;
    font-size: 1.4rem;
    font-weight: 700;
    border-radius: 40px;
    cursor: pointer;
    transition: all 0.3s;
    box-shadow: 0 12px 30px rgba(0, 122, 255, 0.25);
    width: auto;
    max-width: 100%;
}

.buy-button:hover {
    transform: translateY(-3px);
    box-shadow: 0 20px 40px rgba(0, 122, 255, 0.3);
    background: color-mix(in srgb, var(--primary-color) 90%, black);
}

.buy-button:active {
    transform: translateY(0);
}

.buy-button:disabled {
    background: #ccc;
    cursor: not-allowed;
    box-shadow: none;
    transform: none;
}

.secure-info {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    margin-top: 2rem;
    font-size: 0.95rem;
    color: #666;
}

.terms-acceptance {
    margin: 2rem 0;
    padding: 1.5rem;
    background: white;
    border: 1px solid var(--border-color);
    border-radius: 12px;
}

.terms-acceptance label {
    display: flex;
    align-items: flex-start;
    cursor: pointer;
    line-height: 1.6;
    gap: 0.75rem;
}

.terms-acceptance input[type="checkbox"] {
    margin: 0;
    margin-top: 0.25rem;
    min-width: 18px;
    width: 18px;
    height: 18px;
    cursor: pointer;
    flex-shrink: 0;
}

.terms-acceptance span {
    flex: 1;
    font-size: 0.95rem;
}

.terms-acceptance a {
    color: var(--primary-color);
    text-decoration: underline;
}

.terms-acceptance a:hover {
    color: color-mix(in srgb, var(--primary-color) 80%, black);
}

@media (max-width: 1100px) {
    .lesson-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .payment-form {
        padding: 3rem 4rem;
    }
}

@media (max-width: 768px) {
    .payment-form {
        padding: 3rem 2.5rem;
    }
    
    .lessons-header .title {
        font-size: 2.75rem;
    }
    
    .lessons-header .description {
        font-size: 1.15rem;
    }
}

@media (max-width: 600px) {
    .payment-form {
        padding: 2rem var(--margin);
        border-radius: 16px;
        margin: 1rem auto;
    }
    
    .lesson-grid {
        grid-template-columns: 1fr;
    }
    
    .buy-button {
        width: 100%;
        padding: 16px 24px;
        font-size: 1.25rem;
    }
    
    .form-group {
        max-width: 100%;
    }
}