wordpress CSS styles – footer border do not show

I have made simple wordpress layout and the border-bottom in footer do not show. Here is the part of the code of my style.css file:

.site-header {
    border-bottom: 2px solid #999;
}

.site-footer {
    border-top: 20px solid #999;
}

The header border shows correctly but the footer doesn’t. Thank you for any ideas.

Do you have add below the class ?

“site-footer”

In footer section like

<header class="site-header">

Please check.