What is the difference of using:

SPSecurity.RunWithElevatedPrivileges(() =>
{
    using (SPWeb web = site.OpenWeb())
    {
        ....
    }
}

with

SPSecurity.RunWithElevatedPrivileges(delegate()
{
    using (SPWeb web = site.OpenWeb())
    {
        ....
    }
}

the first code not work, but the second code if it works.

what is the difference between the second code works and the another not?

SharePoint 2013 on-premise

What is the difference of using:

SPSecurity.RunWithElevatedPrivileges(() =>
{
    using (SPWeb web = site.OpenWeb())
    {
        ....
    }
}

with

SPSecurity.RunWithElevatedPrivileges(delegate()
{
    using (SPWeb web = site.OpenWeb())
    {
        ....
    }
}

the first code not work, but the second code if it works.

what is the difference between the second code works and the another not?