:root {
    --primary-color: #0056b3;
    --secondary-color: #007bff;
    --bg-color: #f8f9fa;
    --card-bg-color: #ffffff;
    --text-color: #343a40;
    --light-text-color: #6c757d;
    --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: 400px; margin: 1rem auto 2rem; }

/* --- ESTILOS DA CALCULADORA --- */
.calculator {
    background-color: var(--text-color);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    box-shadow: 0 10px 20px rgba(0,0,0,0.2);
}

.calculator-display {
    background-color: #e9ecef;
    color: var(--text-color);
    font-size: 2.5rem;
    font-family: monospace, sans-serif;
    padding: 1rem 1.5rem;
    text-align: right;
    border-radius: var(--border-radius);
    margin-bottom: 1.5rem;
    word-wrap: break-word;
    word-break: break-all;
    min-height: 70px;
}

.calculator-keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1rem;
}

.calculator-keys button {
    padding: 1.25rem 0;
    font-size: 1.5rem;
    font-weight: 600;
    border: none;
    border-radius: var(--border-radius);
    background-color: #6c757d;
    color: white;
    cursor: pointer;
    transition: background-color 0.2s ease;
}

.calculator-keys button:hover {
    filter: brightness(1.2);
}
.calculator-keys button:active {
    filter: brightness(0.9);
}

/* --- CLASSES DE TECLAS --- */
.calculator-keys .key-func {
    background-color: #495057; 
}

.calculator-keys .key-op { /* AC e DEL */
    background-color: #adb5bd;
    color: var(--text-color);
}

.calculator-keys .key-op-main { /* Operadores principais */
    background-color: var(--secondary-color);
}

.calculator-keys .key-equal { /* Botão de Igual */
    background-color: #28a745;
    grid-column: span 3; /* Ocupa 3 colunas */
}

.calculator-keys .key-zero {
    grid-column: span 2;
}

/* --- ESTILOS DO ARTIGO --- */
.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; }

.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; }
}