Exhibit 24

                             2018 POWER OF ATTORNEY

       1.    Appointment, Powers and Revocation.  KNOW ALL MEN BY THESE
PRESENTS, that each undersigned, and if such undersigned is not a natural
person, acting by and through one of its authorized representatives (each such
undersigned person or entity, a "Grantor"), effective from the date set forth
opposite the name of such Grantor on the signature pages hereto (such date, for
each Grantor, is hereinafter referred to as such Grantor's "Effective Date"),
hereby constitutes and appoints each of the employees, partners or managers of
Canaan Management LLC (together with its subsidiaries and affiliates, "Canaan
Partners") listed on Schedule A attached hereto, which schedule may be amended
from time to time by the Chief Financial Officer or Chief Operating Officer of
Canaan Partners to remove any such employee, manager or partner or to add any
new employee, partner or manager of Canaan Partners (each such employee, partner
or manager, an "Attorney-In-Fact") as the Grantor's true and lawful attorney-in-
fact and agent, with full power of substitution and re-substitution, for the
Grantor and in the Grantor's place and stead, in any and all capacities to: (a)
sign any and all instruments, certificates and documents required to be executed
on behalf of the Grantor as an individual (if applicable) or in the Grantor's
capacity as a general partner, manager, member, managing member or authorized
signatory, as the case may be, on behalf of any of the following (i) Canaan
Partners, (ii) any of the funds or accounts managed, advised or sponsored by
Canaan Partners (the "Canaan Funds") and (iii) any of the entities formed to act
as the direct or indirect general partner, manager, managing member or
equivalent of such funds or accounts (the "Canaan General Partners", together
with Canaan Partners and the Canaan Funds collectively, the "Canaan Entities"),
in each case, pursuant to the Securities Act of 1933, as amended, (the
"Securities Act"), and any and all rules and regulations promulgated thereunder
(including, without limitation, filings pursuant to Rule 144 (Form 144)) or the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), and any and
all rules and regulations promulgated thereunder (including, without limitation,
filings pursuant to Section 16 (Forms 3, 4 and 5) and Section 13 (Schedule 13D,
Schedule 13G, Form 13F and Form 13H) of the Exchange Act); and (b) file the
same, with all exhibits thereto, and any other documents in connection
therewith, with the Securities and Exchange Commission, and with any other
entity when and if such is mandated by the Securities Act, the Exchange Act or
by the Financial Industry Regulatory Authority, granting unto such Attorney-In-
Fact full power and authority to do and perform each and every act and thing
requisite and necessary fully to all intents and purposes as the Grantor might
or could do in person thereby, and ratifying and confirming all that such
Attorney-In-Fact, or his or her substitute or substitutes, may lawfully do or
cause to be done by virtue hereof, or may have done in connection with the
matters described above.  By this power of attorney, each Grantor hereby revokes
all previous powers of attorney granted by him, her or it to any Attorney-In-
Fact or any other employee, representative or agent of Canaan Partners relating
to the matters described above.

       2.    Effective Date and Termination.  This power of attorney shall be
effective as to each Grantor as of such Grantor's Effective Date and shall
remain in full force and effect with respect to each Grantor and each Attorney-
In-Fact until:

             (a)    in the case of any Grantor that is an individual, the
earlier of the date on which this power of attorney is revoked in writing by
such Grantor solely as it relates to himself or herself and such Grantor's
Termination Date (as defined below);

             (b)    in the case of any Grantor that is an entity, the earlier of
the date on which this power of attorney is revoked in writing by such Grantor
solely as it relates to itself and the filing by such entity of a certificate of
cancellation or notice of dissolution with the jurisdiction in which it was
organized evidencing such entity's complete dissolution and termination under
the laws of such jurisdiction; and

             (c)    in the case of any Attorney-In-Fact, the earlier of the date
on which such person is no longer listed on Schedule A attached hereto as an
"Attorney-In-Fact" or such Attorney-In-Fact's Termination Date.

For purposes of the foregoing, "Termination Date" means (i) with respect to any
Grantor or Attorney-In- Fact that is a member or manager of any Canaan General
Partner, the date on which such Grantor becomes a "retired member" of any Canaan
General Partner or, if later, the date on which his, her or its employment with
Canaan Partners terminates for any reason and (ii) with respect to any other
Grantor or Attorney-In-Fact, the date on which his, her or its employment with
Canaan Partners terminates for any reason.

       3.    Miscellaneous.  Each of the Grantors may execute this power of
attorney in separate counterparts, and each counterpart shall be deemed to be an
original instrument.  This Agreement shall be governed by the laws of the State
of Delaware, without regard for choice-of-law provisions.

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       IN WITNESS WHEREOF, this Power of Attorney has been signed as of the
respective dates set forth below.


Dated: July 16, 2018             /s/ Timothy M. Shannon
                                 ----------------------
                                 Timothy M. Shannon


                                   Schedule A

Guy M. Russo

Nancy Levenson

Janine MacDonald

John J. Pacifico III