A composition, comprising: a resin component including an olefin-aromatic vinyl compound-aromatic polyene copolymer or an olefin-aromatic polyene copolymer; and a surface-treated silica, and wherein the olefin-aromatic vinyl compound-aromatic polyene copolymer or the olefin-aromatic polyene copolymer_ satisfies all the following conditions to: the number average molecular weight of the copolymer is 500 or more and 100000 or less, measured by the method disclosed in the description; the aromatic vinyl compound monomer is an aromatic vinyl compound having 8 or more and 20 or less carbon atoms, and the content of a unit of the aromatic vinyl compound monomer is 0 mass% or more and 70 mass% or less; the aromatic polyene is one or more selected from polyenes having 5 or more and 20 or less carbon atoms and having a plurality of vinyl groups and/or vinylene groups in the molecule, and the content of the vinyl groups and/or the vinylene groups derived from the unit of the aromatic polyene is 1.5 pieces or more and less than 20 pieces per number average molecular weight; and the olefin is one or more selected from olefins having 2 or more and 20 or less carbon atoms, and the total of units of the olefin monomer, the aromatic vinyl compound monomer, and the aromatic polyene monomer is 100 mass%, wherein the volume ratio between the resin component and the silica is in the range of 85 to 15: 15 to 85, wherein a cured product of the composition has the value of dielectric tangent obtained by resonator method at a measurement frequency of 10 GHz and/or a measurement frequency range of 25 GHz to 40 GHz of 1.2×10 -3 or less, and wherein the cured product of the composition has a storage elastic modulus at 250°C in the range of 10 MPa or more and 10 GPa or less, measured by the method disclosed in the description. a resin component including an olefin-aromatic vinyl compound-aromatic polyene copolymer or an olefin-aromatic polyene copolymer; and a surface-treated silica, and wherein the olefin-aromatic vinyl compound-aromatic polyene copolymer or the olefin-aromatic polyene copolymer_ satisfies all the following conditions to: the number average molecular weight of the copolymer is 500 or more and 100000 or less, measured by the method disclosed in the description; the aromatic vinyl compound monomer is an aromatic vinyl compound having 8 or more and 20 or less carbon atoms, and the content of a unit of the aromatic vinyl compound monomer is 0 mass% or more and 70 mass% or less; the aromatic polyene is one or more selected from polyenes having 5 or more and 20 or less carbon atoms and having a plurality of vinyl groups and/or vinylene groups in the molecule, and the content of the vinyl groups and/or the vinylene groups derived from the unit of the aromatic polyene is 1.5 pieces or more and less than 20 pieces per number average molecular weight; and the olefin is one or more selected from olefins having 2 or more and 20 or less carbon atoms, and the total of units of the olefin monomer, the aromatic vinyl compound monomer, and the aromatic polyene monomer is 100 mass%, the number average molecular weight of the copolymer is 500 or more and 100000 or less, measured by the method disclosed in the description; the aromatic vinyl compound monomer is an aromatic vinyl compound having 8 or more and 20 or less carbon atoms, and the content of a unit of the aromatic vinyl compound monomer is 0 mass% or more and 70 mass% or less; the aromatic polyene is one or more selected from polyenes having 5 or more and 20 or less carbon atoms and having a plurality of vinyl groups and/or vinylene groups in the molecule, and the content of the vinyl groups and/or the vinylene groups derived from the unit of the aromatic polyene is 1.5 pieces or more and less than 20 pieces per number average molecular weight; and the olefin is one or more selected from olefins having 2 or more and 20 or less carbon atoms, and the total of units of the olefin monomer, the aromatic vinyl compound monomer, and the aromatic polyene monomer is 100 mass%, wherein the volume ratio between the resin component and the silica is in the range of 85 to 15: 15 to 85, wherein a cured product of the composition has the value of dielectric tangent obtained by resonator method at a measurement frequency of 10 GHz and/or a measurement frequency range of 25 GHz to 40 GHz of 1.2×10 -3 or less, and wherein the cured product of the composition has a storage elastic modulus at 250°C in the range of 10 MPa or more and 10 GPa or less, measured by the method disclosed in the description.