Hey Leslye,
I’ve rewritten the entire margin-width mechanism in Ikebana for you, please download this custom file, unzip it, and upload the contained files into the theme folder (/wp-content/themes/Ikebana/), replacing the existing files. The content width is now set by a script depending on the size and number of the boxes, while the margins are automated by the CSS. This is the best one can do here, otherwise the theme will seize being responsive and will not adapt to the
I cannot recreate your second issue (the blinking of the video thumbnails) – could you possibly make a screencast?
Sincerely,
Andrew / Satori Studio