CSS suspended center

<! DOCTYPE HTML > 
< HTML lang = "EN" > 
< head > 
    < Meta charset = "UTF-. 8" > 
    < title > Percentage & suspension bar </ title > 
    <-! Almost all of the width can be in percentage represents !! border, line-height is not -> 
    < style type = "text / CSS" > 
        .box { 
            width : 90% ; 
            background-Color : Gray ; 
            border : 0px solid #000;
            left-margin : -45% ; 
            / *     margin width values corresponding to a negative half value     * / 
            font-size : 16px ; 
            / *   line high default * / 
            position : Fixed ; 
            Top : 0% ; 
            left : 50% ; 
            / *     left value is always equal to 50% (if desired centered) * / 
            text-align = left : Center ; 
            Color : #fff ; 
            / * 
            . omitted or directly margin 
            left = (100% -width percentage) divided by 2
            */
        }
        .text{
            width: 30%;
            margin: 2% auto 2%;
            font-weight: bold;
            background-color: lime;
            text-align: center;    
        }
/*        .pop_windows{
            width:     60%;    
            height: 50%;
            margin-left: -30%;
            background-color: #ffff90;
            border: 2px solid #000f;
            text-align: center;
            position: fixed;
            top: 25%;
            left: 50%;
        }*/
        .pop_con{
            display: block;
            /*display: none;*/

        }

        .pop_windows{
            width:     60%;    
            height: 50%;
            /*margin-left: -30%;*/
            background-color: #ffff90;
            border: 2px solid #000f;
            text-align: center;
            position: fixed;
            top: 25%;
            left: 20%;
            z-index: 999;
        }
        .pop_windows h3{
            line-height: 250px; 
        }
        
        .pop_mask{
            width: 100%;
            height: 100%;
            position: fixed;
            top: 0;
            left: 0;
            opacity: 0.3;
            background-color: black;
            z-index: 998;
        }


    </style>
</head>
<body>
    <div class="box">悬浮栏</div>
    <div class="pop_con">    
        <div class="pop_windows">
            <h3><a href="#"></Clicka></h3>
        </div>
        <div class="pop_mask"></div>
    </div>    
    <div class="text">
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    </div>
</body>
</html>
CSS suspended center

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