When I input the following code to solve this system of equations (I specifically want to look at 0<d<1, 0<q<1, 0<t), I get the error:

'DSolve: The function y[t] was specified without dependence on all the independent variables. Each function must depend on all the independent variables.'

Here is my code:

  DSolve[{y'[t] == 1 - q x[t] - (3 + 2 d) y[t], x'[t] == 1 - d y[t] - (3 + 2 q) x[t], x[0] + y[0] == 1}, y[t], x[t], t]

What is the appropriate way to go about solving these differential equations?