SharePoint 2013 by default applies corev15.css to all pages, so you don't need to make a copy and append your styles.

Instead put only your custom CSS into your own corev15.css file and set the link (as you already did).

SharePoint 2013 will then load the default corev15.css and afterwards load your custom one and apply the changes your made.

UPDATE

Just to clarify, you still need a reference to your custom CSS like this:

<!--PS: Start of READ-ONLY PREVIEW (do not modify) --><link href="generalglassintl.sharepoint.com/Style Library/custom/corev15.css" rel="stylesheet" type="text/css"/> and also -> <!--SPM:<SharePoint:CssRegistration Name="/Style Library/custom/corev15.css" runat="server"/>-->

But inside your "/Style Library/custom/corev15.css" you'd only need to put the CSS you want to apply to change the look & feel of the top navigation bar.

SharePoint 2013 by default applies corev15.css to all pages, so you don't need to make a copy and append your styles.

Instead put only your custom CSS into your own corev15.css file and set the link (as you already did).

SharePoint 2013 will then load the default corev15.css and afterwards load your custom one and apply the changes you made.

UPDATE

Just to clarify, you still need a reference to your custom CSS like this:

<!--PS: Start of READ-ONLY PREVIEW (do not modify) --><link href="generalglassintl.sharepoint.com/Style Library/custom/corev15.css" rel="stylesheet" type="text/css"/> and also -> <!--SPM:<SharePoint:CssRegistration Name="/Style Library/custom/corev15.css" runat="server"/>-->

But inside your "/Style Library/custom/corev15.css" you'd only need to put the CSS you want to apply to change the look & feel of the top navigation bar.

SharePoint 2013 by default applies corev15.css to all pages, so you don't need to make a copy and append your styles.

Instead put only your custom CSS into your own corev15.css file and set the link (as you already did).

SharePoint 2013 will then load the default corev15.css and afterwards load your custom one and apply the changes your made.

SharePoint 2013 by default applies corev15.css to all pages, so you don't need to make a copy and append your styles.

Instead put only your custom CSS into your own corev15.css file and set the link (as you already did).

SharePoint 2013 will then load the default corev15.css and afterwards load your custom one and apply the changes your made.

UPDATE

Just to clarify, you still need a reference to your custom CSS like this:

<!--PS: Start of READ-ONLY PREVIEW (do not modify) --><link href="generalglassintl.sharepoint.com/Style Library/custom/corev15.css" rel="stylesheet" type="text/css"/> and also -> <!--SPM:<SharePoint:CssRegistration Name="/Style Library/custom/corev15.css" runat="server"/>-->

But inside your "/Style Library/custom/corev15.css" you'd only need to put the CSS you want to apply to change the look & feel of the top navigation bar.