:root {
    --primary: #2563eb; /* Professional Blue */
    --secondary: #1e40af;
    --accent: #f59e0b; /* Call to action color */
    --bg: #f8fafc;
    --text: #1e293b;
    --white: #ffffff;
    --border: #e2e8f0;
}

* { box-sizing: border-box; margin: 0; padding: 0; font-family: 'Segoe UI', sans-serif; }

body { background-color: var(--bg); color: var(--text); line-height: 1.6; display: flex; flex-direction: column; min-height: 100vh; }

/* Header */
header { background: var(--white); box-shadow: 0 2px 10px rgba(0,0,0,0.05); position: sticky; top: 0; z-index: 1000; }
.navbar { max-width: 1200px; margin: 0 auto; padding: 1rem; display: flex; justify-content: space-between; align-items: center; }
.logo { font-size: 1.5rem; font-weight: 700; color: var(--primary); text-decoration: none; }
.nav-links a { margin-left: 20px; text-decoration: none; color: var(--text); font-weight: 500; transition: color 0.3s; }
.nav-links a:hover { color: var(--primary); }

/* Main Container */
.container { max-width: 1200px; margin: 2rem auto; padding: 0 1rem; flex: 1; display: flex; gap: 2rem; flex-wrap: wrap; }

/* Main Content Area */
.main-content { flex: 2; min-width: 300px; }
.sidebar { flex: 1; min-width: 300px; }

/* Calculator Card */
.calc-card { background: var(--white); padding: 2rem; border-radius: 12px; box-shadow: 0 4px 6px rgba(0,0,0,0.05); border: 1px solid var(--border); }
.form-group { margin-bottom: 1.5rem; }
.form-group label { display: block; margin-bottom: 0.5rem; font-weight: 600; }
.form-control { width: 100%; padding: 0.8rem; border: 1px solid var(--border); border-radius: 8px; font-size: 1rem; transition: border 0.3s; }
.form-control:focus { outline: none; border-color: var(--primary); }

.btn-calc { background: var(--primary); color: var(--white); border: none; padding: 1rem; width: 100%; border-radius: 8px; font-size: 1.1rem; font-weight: 700; cursor: pointer; transition: background 0.3s; }
.btn-calc:hover { background: var(--secondary); }

/* Results Section */
.result-box { margin-top: 2rem; background: #eff6ff; padding: 1.5rem; border-radius: 8px; border-left: 5px solid var(--primary); display: none; }
.result-item { display: flex; justify-content: space-between; margin-bottom: 0.5rem; font-size: 1.1rem; }
.result-total { font-weight: 700; color: var(--primary); font-size: 1.5rem; margin-top: 1rem; border-top: 1px solid #bfdbfe; padding-top: 1rem; }

/* Footer */
footer { background: var(--white); padding: 2rem 1rem; margin-top: auto; border-top: 1px solid var(--border); text-align: center; }
.footer-links a { color: var(--text); margin: 0 10px; text-decoration: none; font-size: 0.9rem; }

/* Ad Placeholder Styles */
.ad-slot { background: #e2e8f0; width: 100%; height: 250px; display: flex; align-items: center; justify-content: center; color: #64748b; font-size: 0.9rem; border-radius: 8px; margin-bottom: 2rem; }

/* Mobile Responsive */
@media (max-width: 768px) {
    .container { flex-direction: column; }
    .nav-links { display: none; /* Add a toggle menu JS if needed for strict mobile */ } 
    /* Ideally use a hamburger menu, but for simplicity keeping it clean */
    .nav-links.active { display: flex; flex-direction: column; position: absolute; top: 60px; left: 0; width: 100%; background: white; padding: 1rem; box-shadow: 0 4px 6px rgba(0,0,0,0.1); }
    .nav-links a { margin: 10px 0; }
}