/* <system section="theme" selected="darkroom"> */
@import "/css/theme/darkroom/darkroom.css";
/* </system> */
.header-image-only #blog-title #blog-title-inner {
height: 400px;
#blog-title {
margin: 0 auto;
padding: 0;
#blog-title-inner{background-size:cover;
}
CSSはこう記述されています