I am trying to vertically center some text in a element, in relation to a much larger that is a sibling of the first one.
If you want the left one-line text to align to the first line of multi-line text on the right, you need to use vertical-align: baseline instead of vertical-align: middle along with display: table-cell. .previewLabel doesn't need a set line-height.
DEMO
.previewLabel {
vertical-align: baseline;
}
span {
display:table-cell;
}
Adding vertical-align:middle to both .previewLabel and .previewText will work just fine.
And here is a fiddle for proof: http://jsfiddle.net/pavloschris/5chXG/4/