About text reflow

In epub, when changing text size or window size, the text is repositioned, but this is not working properly.
Check the attached image. The first and last lines of the page have the text cut in half. This can all be displayed by resizing the window, but since we do not always use the same text size or window size, we will have to adjust it frequently.
In addition, the image shows vertically aligned text, but the beginning of the line is aligned at the bottom. This is not the case with vertical text, which is correctly aligned at the top.