It is not possible to set this directly. First of all, in regards to the width, 80% of what? The Layout containing the widget?
As a suggestion for this, You can use a vertical Layout with either a header and a footer. For these, you can setup a static height of 300 px. Further on, you divide them with another layout (horizontal) with two columns and one of the columns you make it 80% (the other will be 20%). Therefore the widget you will add in the 80% column (it needs to be a responsive widget), will take up 80% of the width of the page and will be forced to have a height of 300 px.
I hope this workaround helps you with your scenario.
Thanks for your suggestion,but maybe it's not what I want. If I use this way, I can't slidedown the page as a whole,and I with I could do something just like this:
<table width="80%" height="300px" > ...... </table>
we can achieve that in html5 code.
I wish the widget could work in panel,for example, when the width of panel is 400px,then the widget's width is 320px,after I change the width of panel to 1000px,the widget's width become 800px automatically.
Is there any way?
In fact ,I want to develop a page like this: bioipsum.
If I use layout,I can only display my contents on the current page and I can't slide down the page as a whole,
If I use panel,I can't make it adaptive.
I have tried many ways but still failed.
Do you have any ideas?
Thanks for your answer.
This kind of web page can't be build with standard TW Mashups, the only scrollable way it's with Repeaters or Dashboards, but you won't get closer to this kind of web page.
You always can build your own web page ( for instance with Bootstrap ) which calls TW REST API, but then your IoT App development won't be as fast as been done with Mashups.