Hello Yeliz.
Easy option: Install this plugin: https://www.ads-software.com/plugins/simple-custom-css/
Then on the plugin’s settings page add the follow CSS elements and then change the properties to your requirements.
For the header
.top-bar {
padding: 10px;
border-top: 4px solid #0088cc;
border-bottom: 4px solid #0088cc;
background: #000;
margin-bottom: 10px;
}
For the footer
#footer {
border-top: 4px solid #0088cc;
background: #000;
color: #f4f4f4;
}
All of the theme’s CSS are located in custom.css and style.css under the css folder. You can use the above method for most of the elements you want to change.
If however the amount of changes you want to make is high then I’d recommend going for a little bit more technical option of creating a child theme and your changes there.
Hope that helps,
Zulf