Hi Janek,
The page header add-on for the blog page is actually in the customizer as WordPress ignores all metabox on index pages: https://docs.generatepress.com/article/blog-page-header/
As for the button, here are the CSS you will need:
.button.see-through {
background-color: transparent;
color: #222
font-weight: 700;
border: 2px solid #2A3949;
}
.button, .button:visited {
display: inline-block;
padding: 10px 15px;
font-size: 17px;
margin-bottom: 5px;
}
.login-button.button.see-through {
background: #FFF;
margin: 0;
width: 100%;
-moz-box-sizing: border-box;
-webkit-box-sizing: border-box;
box-sizing: border-box;
text-align: center;
}
Make sure that you include these three classes: button see-through login-button
More info on buttons here: https://docs.generatepress.com/article/adding-buttons/
Let me know.