Final answer:
The declaration in the CSS rule '.error_text { color: red; }' is the part within the curly braces: '{ color: red; }'. It contains the property 'color' and its value 'red', which styles the selected elements.
Step-by-step explanation:
In the CSS rule .error_text { color: red; }, the declaration is the part that contains the property and value which defines how the selected element should be styled. In this case, it's { color: red; }. The rule is composed of a selector (.error_text) and a declaration block. The declaration itself includes a property (color) and a value (red), specifying that the text color of the element(s) with class 'error_text' should be red.
The declaration in CSS is .error_text { color: red; }. In this rule, .error_text is the selector, which selects the HTML elements that will be affected by the rule. The declaration { color: red; } sets the color property of the selected elements to red. It is important to note that the declaration is enclosed in curly brackets {}.