掲題のカスタマイズ・・追加CSSに追加した内容：下記を記録しました
.site-header {border:0px solid #0f0;
position:fixed;
width:100%;
height:60px;
top:0px;
background:rgba(255,247,234,0.8);
/#ffefcc;/
z-index:9999;
}
.admin-bar .site-header {
position:fixed;
top:32px!important;
}
.site-branding {border:0px solid #a00;
position:fixed;
left:20%!important;}
.main-navigation {border:0px solid #00a;
position:fixed;
left:45%!important;
}
.content-area {padding-top:55px;}
.sticky .card-body {border:0px solid #333;background:#fffcfc!important;}
.rpwwt-widget {padding-top:15px;}
.widget_text {font-size:22px!important;padding-bottom:0px!important;font-weight:bold;}
.wp-calendar-table tr th:first-child {color:#a00;}
.wp-calendar-table tr th:last-child {color:#00f}
.wp-calendar-table #today {background:#fea;}
.wp-calendar-table td:first-child {color:#f00;}
.wp-calendar-table td:last-child {color:#00f;}
.wp-calendar-table tr th {background:#fdf7ed;}
.wp-block-latest-posts__featured-image img {
height:150px!important;
width:90px!important;
}
.rpwwt-widget li {
border:0px solid #ddd;
margin-top:-18px!important;
font-size:10pt;
}
.popular-posts img {width:75px;height:75px;}
.popular-posts {font-size:14px;}