Why can’t color the border-top with red twetyfourteen theme?

Hello @elearn2014,

The Top primary menu has a fixed position and is therefore located on top of the border. In order to make the border visible you need to add the following CSS code:

.masthead-fixed .site-header {
    top: 4px;
}

Please note that if you adjust the width of your border, you also need to adjust the top distance, e.g.

#page {
    border: 10px solid red !important;
}

.masthead-fixed .site-header {
    top: 10px;
}