Kutu.kv

<ScreenManagement>:
    MenuScreen:
        name: 'menu'
    CalculatorScreen:
        name: 'calculator'
    SecondScreen:
        name: 'screen 2'

<MenuScreen>:
    BoxLayout:
        cols: 3
        rows: 2
        Button:
            text: 'Goto\nBasic Calculator'
            multiline: True
            on_press: root.manager.current = 'calculator'
        Button:
            text: 'Screen 2'
            on_press: root.manager.current = 'screen 2'

<CalculatorScreen>:
    Calculator:

<CustButton@Button>:
    font_size: 32
    background_color: 0,0,0,0
    canvas.before:
        Color:
            rgba: ( .44, .50, .56, .7) if self.state=='normal' else (0,.7,.7,1)
        RoundedRectangle:
            pos: self.pos
            size: self.size
            radius: [18, ]

<RawLayout@BoxLayout>:
    spacing: 8
    padding: 5
    size_hint: [1, .5]

<Calculator>:
    id: calculator
    rows: 10
    display: entry
    spacing: 1

    BoxLayout:
        size_hint: [1, .2]
        Label:
            text: 'Basic Calculator'
        Label:
            text: 'Made by Xrew'

    BoxLayout:
        padding: 8
        TextInput:
            id: entry
            spacing: 1
            padding: 5
            font_size: 32
            multiline: True
            focus: False
            halign: 'center'
            background_normal: ' '
            background_color: [.92, 1, 0.9, 1]

    RawLayout:
        CustButton:
            text: 'Exit'
            on_release: root.manager.current = root.manager.previous()
        CustButton:
            text: '<'
            on_press: entry.text += self.text
        CustButton:
            text: '>'
            on_press: entry.text += self.text
        CustButton:
            text: '≈'
            on_press: entry.text += '=='
        CustButton:
            text: '≠'
            on_press: entry.text += '!='

        CustButton:
            text: 'RMD'
            on_press: entry.text += '%'

    RawLayout:
        orientation: 'horizontal'
        CustButton:
            text: '('
            on_press: entry.text += '('
        CustButton:
            text: ')'
            on_press: entry.text += ')'
        CustButton:
            text: '√x'
            on_press: entry.text += '**(.5)'
        CustButton:
            text: '¹/x'
            on_press: entry.text += '1/'
    RawLayout:
        orientation: 'horizontal'
        CustButton:
            text: 'DEL'
            canvas.before:
              Color:
                   rgba: (1, .3, .4, .85) if self.state=='normal' else (0,.7,.7,1)
                RoundedRectangle:
                  pos: self.pos
                   size: self.size
                    radius: [18, ]
            on_press: entry.text = entry.text[:-1]
        CustButton:
            text: 'x²'
            on_press: entry.text += '**2'
        CustButton:
            text: 'xⁿ'
            on_press: entry.text += '**'
        CustButton:
            text: 'π'
            on_press: entry.text += '3.14'

    RawLayout:
        orientation: 'horizontal'
        cols: 4
        CustButton:
            text: 'CLR'
            background_color: 0,0,0,0
            canvas.before:
              Color:
                   rgba: (1, .3, .4, .85) if self.state=='normal' else (0,.7,.7,1)
                RoundedRectangle:
                  pos: self.pos
                   size: self.size
                    radius: [18, ]
         #   background_normal: ' '
           #  background_color: 1, .3, .4, .85
            on_press: entry.text = ""
        CustButton:
            text: 'F.Dv'
            on_press: entry.text += '//'
            font_size: 32
        CustButton:
            text: '÷'
            on_press: entry.text += '/'
        CustButton:
            text: '×'
            on_press: entry.text += '*'

    RawLayout:
        rows: 1
        orientation: 'horizontal'
        CustButton:
            text: '7'
            on_press: entry.text += self.text
        CustButton:
            text: '8'
            on_press: entry.text += self.text
        CustButton:
            text: '9'
            on_press: entry.text += self.text
        CustButton:
            text: '-'
            on_press: entry.text += self.text

    RawLayout:
        orientation: 'horizontal'
        rows: 1
        CustButton:
            text: '4'
            on_press: entry.text += self.text
        CustButton:
            text: '5'
            on_press: entry.text += self.text
        CustButton:
            text: '6'
            on_press: entry.text += self.text
        CustButton:
            text: '+'
            on_press: entry.text += self.text

    RawLayout:
        orientation: 'horizontal'
        cols: 3
        CustButton:
            text: '1'
            size_hint: [.5, 1]
            on_press: entry.text += self.text
        CustButton:
            text: '2'
            size_hint: [.5, 1]
            on_press: entry.text += self.text
        CustButton:
            text: '3'
            size_hint: [.5, 1]
            on_press: entry.text += self.text
        CustButton:
            text: ' '
            size_hint: [.5, 1]
            background_normal: ' '
            background_color: .3, .3, .3, 1

    RawLayout:
        orientation: 'horizontal'
      #  size_hint: [1, .2]
        CustButton:
            text: '0'
            on_press: entry.text += self.text
            size_hint: [.34, 1]
        CustButton:
            text: '.'
            on_press: entry.text += self.text
            size_hint: [.17, 1]
            font_size: 32
        CustButton:
            text: '='
            on_press: calculator.calculate(entry.text)
            size_hint: [.17, 2.15]
            canvas.before:
                Color:
                    rgba: (0, 255, 255, 1 ) if self.state == 'normal' else (0,0,255,1)
                RoundedRectangle:
                    pos: self.pos
                    size: self.size
                    radius: [18, ]

<SecondScreen>:
    BoxLayout:
        orientation: 'horizontal'
        size_hint: [1, .1]
        Button:
            text: 'BMI'
        Button:
            text: 'BMR'
        Button:
            text: '1MR'
        Button:
            text: 'Exit'
            on_release: root.manager.current = root.manager.previous()