/**
 * base.css - Reset, body, container, header
 *
 * Phong cách cơ bản cho:
 *   - Reset CSS (* margin/padding/box-sizing)
 *   - body: font, background gradient, min-height
 *   - .container: bao bọc nội dung
 *   - .header: tiêu đề trang với gradient xanh đậm
 */

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

body { font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', 'SF Pro Display', Roboto, 'Helvetica Neue', Arial, sans-serif; background: linear-gradient(135deg, #f5f7fa 0%, #e4ecf3 100%); color: #1a2332; line-height: 1.55; padding: 16px; min-height: 100vh; }

.container { max-width: 1200px; margin: 0 auto; }

.header { background: linear-gradient(135deg, #0f4c75 0%, #1a5f8e 100%); color: white; padding: 24px 28px; border-radius: 12px; box-shadow: 0 4px 12px rgba(15,76,117,0.2); margin-bottom: 16px; }

.header h1 { font-size: 22px; margin-bottom: 6px; font-weight: 700; }

.header .subtitle { font-size: 13px; opacity: 0.92; line-height: 1.5; }