[Modal] .mui-fixed issue with border-box

• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

Elements with postition: fixed;, right: 123px and .mui-fixed class applied doesn’t move on Modal open

Current Behavior

it moves, because additional padding doesn’t affect element with right position

Steps to Reproduce (for bugs)

Reproducer:

Context

Your Environment

Tech	Version
Material-UI	1.0.0-beta.21
React	16.0.0
browser	Firefox-57, Chrome-62
etc

[oliviertassinari]

This is interesting, your example doesn’t work:

        <Button
          className="mui-fixed"
          style={{
            position: "fixed",
            right: "10px",
            backgroundColor: "pink"
          }}
          onTouchTap={this.openPopoverAvatar}
          aria-owns="simple-menu"
          aria-controls="simple-menu"
          aria-haspopup="true"
        >
          show popover
        </Button>

But this variation does. It’s the solution I would encourage to use:

        <div
          className="mui-fixed"
          style={{
            position: "fixed",
            right: "10px"
          }}
        >
          <Button
            style={{
              backgroundColor: "pink"
            }}
            onClick={this.openPopoverAvatar}
            aria-owns="simple-menu"
            aria-controls="simple-menu"
            aria-haspopup="true"
          >
            show popover
          </Button>
        </div>

[oliviertassinari]

I have updated the reproduction to use Material-UI v4.5.2: https://codesandbox.io/s/priceless-satoshi-5g8rv. The problem was solved.