Widget Label Sizing

from IPython.html.widgets import FloatTextWidget, ButtonWidget, ContainerWidget, HTMLWidget
from IPython.html.widgets.widget import CallbackDispatcher
from IPython.utils.traitlets import Unicode, Instance

class VideoParameterWidget(ContainerWidget):
    description = Unicode(sync=True)
    value = Instance(object, sync=True)

    def __init__(
        self,
        description=u'',
        params=None,
        **kwargs
    ):
        super(VideoParameterWidget, self).__init__(description=description, **kwargs)
        self.description = description
        self.value = {
            p['name']: p['value']
            for p in params
        }
        self.children = [
            FloatTextWidget(description=p['description'] + ':', value=p['value'])
            for p in params
        ]
        self.submissionCallbacks = CallbackDispatcher()
        self.cancelCallbacks = CallbackDispatcher()
        # instructions widget
        self.insw = HTMLWidget(value=self.toHTML(''))
        # Done button
        self.donew = ButtonWidget(description='Done')
        self.donew.on_click(self.submit)
        # Cancel button
        self.cancelw = ButtonWidget(description='Cancel')
        self.cancelw.on_click(self.cancel)
        self.cancelw.visible = False
        self.binsw = ContainerWidget()    # top row
        self.binsw.on_displayed(self.sideBySide)
        self.binsw.children = [self.insw, self.donew, self.cancelw]
        self.children = (self.binsw,) + self.children
        self.setInstructions("Set Parameter Values:")
        self.on_displayed(self.onDisplay)

    def onDisplay(self, name=None):
        self.sideBySide(name)

    def sideBySide(self, name=None):
        """Arrange children horizontally."""
        self.binsw.remove_class('vbox')
        self.binsw.add_class('hbox')
        # self.binsw.set_css('width', '100%')
        self.binsw.add_class('center')

    def toHTML(self, text):
        """Convert text to HTML."""
        html = '<table><tr height=40><th width=15 />\n'
        html += '<th style=\"vertical-align: center;\"><b>' + text + '</b></th>'
        html += '<th width=15 /></tr></table>'
        return html

    def setInstructions(self, text):
        self.insw.value = self.toHTML(text)

    def submit(self, name=None):
        """
        Calculate and submit results when Done button clicked.

        This is more-or-less an abstract method. You should override
        it, but call the superclass method AFTER you have set
        self.value correctly.
        """
        self.send('value')
        self.submissionCallbacks(self)

    def cancel(self, name=None):
        """Fire cancel callbacks."""
        self.cancelCallbacks(self)

    def on_submit(self, callback, remove=False):
        """
        (Un)Register a callback to handle result submission.

        Triggered when the user clicks the Done button.

        Parameters
        ----------
        callback: callable
            Will be called with exactly one argument: the Widget instance
        remove: bool (optional)
            Whether to unregister the callback
        """
        self.submissionCallbacks.register_callback(callback,
                                                   remove=remove)

    def on_cancel(self, callback, remove=False):
        """
        (Un)Register a callback to cancel calibration.

        Triggered when the user clicks the Cancel button. (The Cancel
        button will not appear until a callback is registered.)

        Parameters
        ----------
        callback: callable
            Will be called with exactly one argument: the Widget instance
        remove: bool (optional)
            Whether to unregister the callback
        """
        self.cancelw.visible = True
        self.cancelCallbacks.register_callback(callback,
                                               remove=remove)

params = [{'description': 'Expected Worm Width',
  'name': 'expectedWormWidth',
  'value': 70},
 {'description': 'Expected Worm Length',
  'name': 'expectedWormLength',
  'value': 1000},
 {'description': 'Worm Area Threshold Lower Bound',
  'name': 'wormAreaThresholdLB',
  'value': 0.5},
 {'description': 'Worm Area Threshold Upper Bound',
  'name': 'wormAreaThresholdUB',
  'value': 1.5},
 {'description': 'Number of Posture Points',
  'name': 'numberOfPosturePoints',
  'value': 30},
 {'description': 'Background Disk Radius',
  'name': 'backgroundDiskRadius',
  'value': 5},
 {'description': 'Threshold', 'name': 'threshold', 'value': 0.9},
 {'description': 'Worm Disk Radius', 'name': 'wormDiskRadius', 'value': 2}]


vpw1 = VideoParameterWidget(
    description='Analysis Parameters',
    params=params
)
def reportCancel(self=None):
    print("Cancelled.")
vpw1.on_cancel(reportCancel)
vpw1