:root{--primary-color: #3498db;--bg-color: #f8f9fa;--text-color: #2c3e50;--border-color: #ddd;--nav-bg: #fff}body{margin:0;font-family:Inter,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen,Ubuntu,Cantarell,Open Sans,Helvetica Neue,sans-serif;background-color:var(--bg-color);color:var(--text-color)}.app-header{background-color:var(--nav-bg);border-bottom:1px solid var(--border-color);padding:0 20px;position:sticky;top:0;z-index:100}.nav-container{max-width:1200px;margin:0 auto;height:60px;display:flex;align-items:center;gap:30px}.nav-item{text-decoration:none;color:var(--text-color);font-weight:500;transition:color .3s,border-bottom .3s;height:60px;display:flex;align-items:center;border-bottom:2px solid transparent}.nav-item:hover{color:var(--primary-color)}.nav-item.active{color:var(--primary-color);border-bottom-color:var(--primary-color)}.app-main{max-width:1200px;margin:20px auto;background:#fff;border-radius:8px;box-shadow:0 2px 12px #0000000d;min-height:calc(100vh - 120px)}