I'm building the backend to a web application, where it is possible to change the design of a page. Once the user has setup the design the way they like it, they should be able to save it and the new design would be written to the specific file. 

For this reason, I will need to replace all the characters between `{` and `}` after a certain string, which would be the name of the class. 

So a very simple concept, say the following class was in a seperate file which I load as a view, style.php. I would need to go from: 

from 

```
<style>
.bonus {
    bottom: 6px;
    left: 247px;
}
</style>

```

to

```
<style>
.bonus {
    bottom: 20px;
    left: 450px;
}
</style>

```

Could someone recommend me on the best way to

a) find a string in a file,

b) when that is found, replace everything between two strings right after the first string.

Thank you.