You have to use a CSS preprocessor for this, like LESS or SASS. You can't do it with pure css. Have a look here: http://lesscss.org/ or here: http://sass-lang.com/ (I use LESS myself)
Extra:
A CSS-only solution to your example would be to use a modular approach in which you define multiple classes for specific attributes which you can re-use in your HTML. I would suggest doing this even when using a CSS preprocessor. So for your example you could make these classes:
.cell {
width: 45%;
min-height: 130px;
}
.cell-left {
}
.cell-right {
}
And then add both the cell and the cell-left / cell-right classes to your HTML elements. This way you only have to declare the width and min-height properties once.
Or, you could do:
.cell-left, .cell-right {
width: 45%;
min-height: 130px;
}
So you only have to change it once as well.