Insert into a table a foreign key I already search in here but i can't found an awnser , i have this code :

CREATE TABLE Aquario(
    ANome varchar(64) PRIMARY KEY,
    Localização varchar(8),
    Capacidade integer(15));


CREATE TABLE Habitat(
    HNome varchar(100) PRIMARY KEY,
    Iluminamento integer(10),
    Salinidade integer(2),
    pH integer(2),
    Dureza integer(3),
    Oxigenação integer(3),
    Temperatura integer(2));

CREATE TABLE contem(
    HNome varchar(64),
    ANome varchar(64),
    Percentagem_de_adequação integer(2),
    PRIMARY KEY (ANome),
    FOREIGN KEY(ANome) REFERENCES Aquario(ANome),
    FOREIGN KEY(HNome) REFERENCES Habitat(HNome));


INSERT INTO contem (Percentagem_de_adequação) VALUES (20);


INSERT INTO Aquario (ANome, Localização, Capacidade) VALUES ('Os Peixes azuis','Este',20);

INSERT INTO  Habitat (HNome, Iluminamento, Salinidade,pH,Dureza,Oxigenação,Temperatura) VALUES ('Os peixes' ,20  ,1 ,5 ,213 ,52,2);


This code don't let  me do the table " contem " why ?
Firstly, your datatypes and precision should always be identical on your FK references. 

In Habitat you have HNome as a VARCHAR(100). In Cotem, you have HNome as a VARCHAR(64).  These need to be the same.

It would help if you would post the error message you are getting, but I suspect the error is you are trying to insert a NULL value into ANome in Cotem.