:root {
    --primary-color: #0056b3;
    --secondary-color: #007bff;
    --bg-color: #f8f9fa;
    --card-bg-color: #ffffff;
    --text-color: #343a40;
    --light-text-color: #6c757d;
    --success-color: #28a745;
    --danger-color: #dc3545;
    --info-color: #17a2b8;
    --border-radius: 12px;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.05), 0 1px 3px rgba(0, 0, 0, 0.08);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Poppins', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
}

.page-header {
    max-width: 700px;
    margin: 0 auto;
    padding: 1.5rem 2rem 0;
}

.btn-back {
    display: inline-block;
    padding: 0.5rem 1rem;
    background-color: #e9ecef;
    color: var(--primary-color);
    text-decoration: none;
    border-radius: var(--border-radius);
    font-weight: 600;
    transition: background-color 0.3s ease;
}

.btn-back:hover {
    background-color: #dee2e6;
}

.container {
    max-width: 700px;
    margin: 1rem auto 2rem;
    padding: 2.5rem;
    background-color: var(--card-bg-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    border: 1px solid #e9ecef;
}

.calculator-header {
    text-align: center;
    margin-bottom: 2rem;
}

.calculator-header h1 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.equation-inputs {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.75rem;
    margin-bottom: 2rem;
    flex-wrap: wrap;
}

.equation-inputs .form-group {
    margin-bottom: 0;
}

.equation-inputs input {
    width: 80px;
    text-align: center;
    font-size: 1.2rem;
    padding: 0.75rem 0.5rem;
}

.equation-inputs span {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--light-text-color);
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    text-align: center;
    font-size: 0.9rem;
}

.form-group input {
    border: 1px solid #ced4da;
    border-radius: var(--border-radius);
    font-family: 'Poppins', sans-serif;
}

.form-group input:focus {
    outline: none;
    border-color: var(--secondary-color);
    box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.25);
}

button[type="submit"] {
    width: 100%;
    padding: 1rem;
    background: linear-gradient(90deg, var(--secondary-color) 0%, var(--primary-color) 100%);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.3s ease;
}

button[type="submit"]:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 10px rgba(0, 86, 179, 0.3);
}

#results-container {
    margin-top: 2.5rem;
    padding-top: 1.5rem;
    border-top: 1px solid #eee;
    text-align: center;
}

#results-container.hidden {
    display: none;
}

#results-summary {
    margin-bottom: 1.5rem;
    font-size: 1.1rem;
}

#results-summary .label {
    color: var(--light-text-color);
}
#results-summary .value {
    font-weight: 600;
    color: var(--primary-color);
}
#results-summary .interpretation {
    display: block;
    font-style: italic;
    margin-top: 0.5rem;
}

#roots-display {
    display: flex;
    justify-content: center;
    gap: 2rem;
    flex-wrap: wrap;
}

.root-card {
    background-color: #e7f5ff;
    padding: 1rem 1.5rem;
    border-radius: var(--border-radius);
    min-width: 150px;
}

.root-card .label {
    font-size: 1rem;
    font-weight: 600;
    color: var(--primary-color);
}

.root-card .value {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--primary-color);
    display: block;
}

.error-message {
    background-color: #fff3f3;
    color: var(--danger-color);
    padding: 1rem;
    border-radius: var(--border-radius);
    font-weight: 600;
}

.explanation-article {
    max-width: 700px;
    margin: 0 auto 2rem;
    padding: 2.5rem;
    background-color: var(--card-bg-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    border: 1px solid #e9ecef;
}

.explanation-article h2, .explanation-article h3 {
    color: var(--primary-color);
    margin-bottom: 1rem;
}

.explanation-article h3 {
    margin-top: 1.5rem;
    border-bottom: 1px solid #eee;
    padding-bottom: 0.5rem;
    font-size: 1.3rem;
}

.explanation-article p, .explanation-article ul {
    margin-bottom: 1rem;
    color: var(--text-color);
}

.explanation-article ul {
    padding-left: 25px;
}

.explanation-article .formula {
    text-align: center;
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--text-color);
    background-color: #f1f3f5;
    padding: 1rem;
    border-radius: var(--border-radius);
}

.main-footer {
    text-align: center;
    padding: 2rem 1rem;
    color: var(--light-text-color);
    font-size: 0.9rem;
}

@media (max-width: 768px) {
    .container, .page-header, .explanation-article {
        margin-left: 1rem;
        margin-right: 1rem;
        padding: 1.5rem;
    }
}