<p>
        When we use the default master, the style sequence is as follow.
        </p>


        <pre data-sub="prettyprint:_">
        <!-- editable, when edit it will unghost to folder _style/core.css -->

        <link href="/_layouts/1033/styles/core.css?rev=5msmprmeONfN6lJ3wtbAlA%3D%3D" type="text/css" rel="stylesheet">
        </link>

        <!-- optional, if we specify alternate css  -->
        <link href="/Documents/fred.css" type="text/css" rel="stylesheet">
        </link>
        <!-- optional, if we specify themes, editable, if edit it will be unghosted -->
        <link id="onetidThemeCSS" href="/_themes/Granite/Gran1011-65001.css?rev=12%2E0%2E0%2E4518" type="text/css" rel="stylesheet">
        </pre>


        <p>
        So we can use still use the css selector in the core.css, but we can override the style in core.css, because the alternate style and theme style come after.
        </p>

        <p>
        If we want use customize customized master page, then we need to take control of all the style.
        </p>