Question: How can we concatenate an expression value with some string and evaluate the resulting expression?

If we have one object prefix and I wanted to concatenate its value with some string. e.g 

```
{{prefix"Output"}}

```

I would like to first evaluate the prefix value and then concatenate it with the "Output" string. 

So the resulting expression may be something like "UnitOutput" where Unit is the value of the prefix.

Lastly I want the concatenated expression from above to be evaluated as well in that case resulting value will be the value of "UnitOutput".

Answer: 
Since you have first run ionic setup sass as mentioned in the answers, you need to search and identify the variable you want override on the file **\_variables.css** and them you will override in **ionic.app.scss**. 

For the bar-stable color i do find into \_variable.scss :

```
$bar-stable-text: $button-stable-text !default; 

```

And override in ionic.app.scss with:

```
$bar-stable-text:                 #FFFFFF !default;

```

This works.
Override this Ionic Sass Variable in themes/variables.scss

```
$toolbar-title: #fff;

```