Module:Message box/styles.css

/* Cell sizes for ambox/tmbox/imbox/cmbox/ombox/fmbox/dmbox message boxes */
th.mbox-text, td.mbox-text {   /* The message body cell(s) */
	border: none;
	/* @noflip */
	padding: 0.25em 0.9em;     /* 0.9em left/right */
	width: 100%;               /* Make all mboxes the same width regardless of text length */
}
td.mbox-image {                /* The left image cell */
	border: none;
	/* @noflip */
	padding: 2px 0 2px 0.9em;  /* 0.9em left, 0px right */
	text-align: center;
}
td.mbox-imageright {           /* The right image cell */
	border: none;
	/* @noflip */
	padding: 2px 0.9em 2px 0;  /* 0px left, 0.9em right */
	text-align: center;
}
td.mbox-empty-cell {           /* An empty narrow cell */
	border: none;
	padding: 0;
	width: 1px;
}

/* These mbox-small classes must be placed after all other
   ambox/tmbox/ombox etc classes. "html body.mediawiki" is so
   they override "table.ambox + table.ambox" above. */
html body.mediawiki .mbox-small {   /* For the "small=yes" option. */
	/* @noflip */
	clear: right;
	/* @noflip */
	float: right;
	/* @noflip */
	margin: 4px 0 4px 1em;
	box-sizing: border-box;
	width: 238px;
	font-size: 88%;
	line-height: 1.25em;
}
html body.mediawiki .mbox-small-left {   /* For the "small=left" option. */
	/* @noflip */
	margin: 4px 1em 4px 0;
	box-sizing: border-box;
	overflow: hidden;
	width: 238px;
	border-collapse: collapse;
	font-size: 88%;
	line-height: 1.25em;
}