"""Validate the structure and content of a script dictionary.

The function checks if the script contains all required sections, ensures each section has both 'text' and 'duration' fields, and verifies that the total duration does not exceed 90 seconds.

Args:
    script (Dict): A dictionary representing the script, where keys are section names and values are dictionaries containing 'text' and 'duration' fields.

Returns:
    Tuple[bool, str]: A tuple where the first element is a boolean indicating whether the script is valid, and the second element is an error message (empty string if valid).

Raises:
    None: This function does not raise any exceptions but returns a tuple with validation results.
"""
You should write code starting with:
from typing import Dict, Tuple

def validate_script(script: Dict) -> Tuple[bool, str]:
    # TODO: Implement this function
    pass

