The party line is it's a "three-legged stool". They know that the Divinely-inspired word of God holds first place in authority then, according to them, and it's followed by Tradition and the Magisterium. If you ask which is the ultimate authority should there be a conflict, the answer is that there can not BE a conflict. ;o)
Because in reality it is the Magisterium that is the supreme authority, which determines what Scripture and Tradition consist of and mean, which she says means she is the supreme authority, and Scripture in particular becomes a servant which can be abused in order to support "The Church," or denied its refutation of her.
While demanding one verse that establishes SS, a multitude of verses are denied as showing its singular supremacy, while an understanding of its material sufficiency is simply ignored as is the fact that her Magisterium does not speak as wholly inspired of God as men such as the apostles could in orally speaking the formal word of God (and yet could be subject to testing by Scripture when they did).
But then Catholics will insist that something like Mary being sinless and a perpetual virgin is Scriptural, even though there is not one verse that actually teaches this very significant exception to the norm, and the Holy Spirit characteristically notes even lesser notable exceptions to the norm among individuals, and affirms the sinlessness of Christ at least thrice.
Meanwhile they deny that the verse "And knew her not till she had brought forth her firstborn son" (Matthew 1:25) denotes a consummation of marriage, which is how Scripture describes it, (Gn. 2:24; Mt. 19:4-6) for they claim another (very very rare) exception to the norm, that the word for "till" does not denote a terminus indicating a change.
To which are added many other distinctive Catholic teachings that are not manifest in the only wholly inspired substantive authoritative record of what the NT church believed (which is Scripture, in particular Acts through Revelation, which best shows how the NT church understood the gospels).
And why do they do this? Because Scripture, Tradition and History only means what Rome says they do. Thus the recourse of no less a prelate as Manning:
“It was the charge of the Reformers that the Catholic doctrines were not primitive, and their pretension was to revert to antiquity. But the appeal to antiquity is both a treason and a heresy. It is a treason because it rejects the Divine voice of the Church at this hour, and a heresy because it denies that voice to be Divine. ” "I may say in strict truth that the Church has no antiquity. It rests upon its own supernatural and perpetual consciousness. Its past is present with it, for both are one to a mind which is immutable. Primitive and modern are predicates, not of truth, but of ourselves.... The only Divine evidence to us of what was primitive is the witness and voice of the Church at this hour." — Dr. Henry Edward Cardinal Manning, Lord Archbishop of Westminster, “The Temporal Mission of the Holy Ghost: Or Reason and Revelation,” (New York: J.P. Kenedy & Sons, originally written 1865, reprinted with no date), pp. 227-228.