You have to reset each individual property back to its default value. It’s not great, but it’s the only way, given the information you’ve given us.
In your example, you would do:
.c1 {
height: auto;
}
You should search for each property here:
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference
For example, height:
Initial value :
auto
Another example, max-height:
Initial value :
none
In 2017, there is now another way, the unset keyword:
.c1 {
height: unset;
}
Some documentation: https://developer.mozilla.org/en-US/docs/Web/CSS/unset
The unset CSS keyword is the combination of the initial and inherit
keywords. Like these two other CSS-wide keywords, it can be applied to
any CSS property, including the CSS shorthand all. This keyword resets
the property to its inherited value if it inherits from its parent or
to its initial value if not. In other words, it behaves like the
inherit keyword in the first case and like the initial keyword in the
second case.
Browser support is good: http://caniuse.com/css-unset-value