How to Center Titles Horizontally in Vertical EPUBs Created with Denden Converter

When creating a vertical EPUB using Denden Converter, it is possible to place book titles or chapter titles on independent pages, but they end up aligned to the right of the page.

I wanted to find a way to center this horizontally on the page, and I have finally figured it out.

Since Denden Converter allows you to upload your own CSS, I tried tweaking the CSS while consulting with ChatGPT. However, to put it simply, modifying the CSS alone did not work. The only method I found was to directly edit the xhtml files of the EPUB using EPUB editing software (it might also work to write html tags directly into the Markdown file).

The modifications are as follows: Once you have created an EPUB with independent title pages using Denden Converter, use EPUB editing software like calibre to wrap the header you want to center within the xhtml file containing the title using <div class="title">. A concrete example is as follows.

     <div class="title"> <!--  追加 -->
        <h1 id="toc_index_1">［私家版］イラストからはじめたショートストーリーズ</h1>
     </div> <!--  追加 --> 

After that, modify the book-style.css file within the EPUB as follows. The example only shows h1, but please modify the header levels you wish to center.

/* CSSファイルに追加 */
.title {
  -epub-writing-mode: horizontal-tb; /* いったん横書きに戻す */
  text-align: center;               /* 横書き状態で「左右中央」を確定させる */
  width: 100%;
}

h1 {
  font-size: 2em;
  margin-right: 0.625em;
  margin-left: 0.625em;
/* 追加部分 */
  -epub-writing-mode: vertical-rl;  /* テキストだけ縦書きに戻す */
  display: inline-block;
/* ここまで */
}

That is all. If corrected properly, the title should now be centered horizontally.

Regarding the previously published "[Private Edition] Short Stories Started from Illustrations," I have replaced it with an EPUB file where the titles are centered, so please feel free to check it out if you are interested. Since publication, I have occasionally corrected typos and replaced the file, so if you downloaded it previously and have just left it as is, please re-download it if you have the time.

The method for creating EPUBs using Denden Converter is summarized below.