moodle/blocks/search_forums/styles.css

.block_search_forums .searchform {
    text-align: center;
}

.block_search_forums .searchform img {
    vertical-align: middle;
}

.block_search_forums .searchform img.resize {
    width: 1em;
    height: 1.1em;
}

.block_search_forums .invisiblefieldset {
    display: block;
}