String.prototype.camelize = function( ) {
  return this.replace( /-([a-z])/g,
      function( $0, $1 ) { return $1.toUpperCase( ) } );
}
String.prototype.deCamelize = function( ) {
  return this.replace( /[A-Z]/g,
      function( $0 ) { return "-" + $0.toLowerCase( ) } );
}

//戻り値 : 挿入したルールの位置を表すインデックス（Number）
function addRule( selector, property, sheetindex, ruleindex ) {
  if( sheetindex == undefined ) sheetindex = 0;
  var sheet = document.styleSheets[ sheetindex ];

  if( sheet.addRule ) { //IE
      if( ruleindex == undefined ) ruleindex = sheet.rules.length;
      sheet.addRule( selector, "{" + property + "}", ruleindex );
      return ruleindex;
  }
  else if( sheet.insertRule ) { //Mozilla
      if( ruleindex == undefined ) ruleindex = sheet.cssRules.length;
      return sheet.insertRule( selector + "{" + property + "}", ruleindex );
  }

  return null;
}

function getWindowHeight(){
  if(window.innerHeight) return window.innerHeight; // Mozilla, Opera, NN4
  if(document.documentElement && document.documentElement.clientHeight){ // 以下 IE
   return document.documentElement.clientHeight;
  }
  else if(document.body && document.body.clientHeight){
   return document.body.clientHeight;
  }
  return 0;
}

if(getWindowHeight() < 580){
	addRule( "#navi", "position:absolute" );
}
else{
	addRule( "#navi", "position:fixed" );
	addRule( "#navi", "_position:absolute" );
	addRule( "body", "background-attachment:fixed" );
}