Trouble with vertically expanding DIVS

Question

(Dreamweaver CS5, MacBook Pro, OS X.8.2)
This issue has bothered me for some time. I have not been able to find a solution on the web as of yet. And yes, I'm fairly new to CSS!
I have two DIVS, side by side, in a wrapper DIV (shown in purple line) to hold them in place left and right. There is also another outer wrapper (called ".main", orange line.) to hold the whole array centered on the page.
What I want is for the text DIVS to expand vertically to accommodate any text overrun in cases of browser render differences.
With that in mind, if I should remove the height specification from the text DIVS (.featureleft and .featureright), the bottom edge of those DIVS will collapse upward until they connect with the last line of their text content, which is of course what I want, because this means, of course, that if I add more text, the DIVs will expand downward to accommodate the additional text.
However, when I remove the height specification from the wrapper (".wrapper", shown in purple), the .wrapper DIV collapses upward all the way to its own top line, in complete disregard of its own contents (.featureleft and .featureright). In other words, it behaves as if it was an empty DIV.
Why does this happen? Why would it ignore its contents? Thank you-
Here is some general code I'm using for the DIV structures:
.main {
    width: 940px;
    margin: 0 auto;
.wrapper {
    width: 940px;
    height: 850px;
.featureleft {
    width: 450px;
    height: 680px;
    font-family: Arial, Helvetica, sans-serif;
    float: left;
    text-align: left;
.featureright {
    width: 450px;
    height: 680px;
    font-family: Arial, Helvetica, sans-serif;
    float: right;
    text-align: left;

Answer 1

Nancy O. wrote:
Height is always determined by content and not explicit height values. ..
Remove height from all containers with text in them...
Nancy O.
If we're on the same sheet of music here, height is determined by either the presence or absence of a value (.featureleft, for example, has a specified height of 680 pixels). That's pretty explicit, I'd say! Perhaps I'm not fully understanding of the point you are trying to convey?
Yes, again when I remove the height values, the text-containing DIVS do exactly what I wish for. However, when I remove the height value from their parent wrapper, that wrapper DIV collapses in on itself (upwards), thus ignoring its contents. Why?