\documentclass[12pt,twoside]{report}
\usepackage[margin=2cm]{geometry}
\usepackage{amsmath,amsthm,amssymb}
\usepackage{thmtools}
\usepackage{tikz}
\usepackage[framemethod=TikZ]{mdframed}
\declaretheoremstyle
[ spaceabove=0pt, spacebelow=0pt, headfont=\normalfont\bfseries,
notefont=\mdseries, notebraces={(}{)}, headpunct={\newline}, headindent={},
postheadspace={ }, postheadspace=4pt, bodyfont=\normalfont, qed=$\blacktriangle$,
mdframed={ outermargin = 1.3cm , %
leftmargin = 0pt , rightmargin = 0pt , %